Preliminary Considerations

Warning: Always work from a copy of your file so you don't make things
worse! If you can't make a copy of the file, see step 7. in the 2nd section.

1. You would be well advised to take a look at Microsoft's articles on the subject first even if you find them confusing. If you have Excel 2002 and 2003, see the MS Office Assistant Article about recovering files:
   http://office.microsoft.com/assistance/preview.aspx?AssetID=HA010346561033&CTT=6&Origin=EC010553071033.
   
   
2. The Microsoft Knowledge Base Articles (more advanced) are here including Excel 97 and 2000 articles. The information does not change much between versions.
   1. For all of Microsoft's Excel 97official methods, including the complicated external file reference method is available here:
   http://support.microsoft.com/default.aspx'scid=KB;en-us;Q142117.
   2. For all the Excel 2000 methods look here:
      http://support.microsoft.com/default.aspx'scid=KB;en-us;Q179871.
   3.  For all the Excel 2002 and 2003 methods look here: http://support.microsoft.com/default.aspx'scid=KB;en-us;Q291057.
      
      
3. This newsgroup post looks good too: http://preview.tinyurl.com/23zdbb.

Another Set of Procedures
Including Obvious Ones

Warning: Always work from a copy of your file so you don't make
things worse!  See step 7. if you can't make a copy of the file.

1. Close down Excel, reopen it and try to open the file again.

2. If this doesn't work, restart the computer, open up Excel and try to open the file again.

3. If this doesn't work, delete the contents of your c:\ Windows\temp directory then reboot. Try again.

4. If this doesn't work, open Excel in Safe Mode. This will disable VBA and Add-ins. Click on Start then Run then enter (including the quotes and the /s extension): "C:\Program Files\Microsoft Office\Office\excel.exe" /s ["C:\Program Files\Microsoft Office\Office10\excel.exe" /s (for Excel 2002, Office XP, click cancel if the MS Office Installer starts, Excel in safe mode will still start)].Try to open the file.

5. If this doesn't work, be sure to scan the file for viruses. Make sure your macro heuristics scanning option is turned on. Ask your IT administrator how to do this.

6. If you don't find a virus, try to open the file in Word.  Note after you do this, you will probably have to make another copy because Word sometimes destroys the binary structure of Excel (I think).

7. If this doesn't work, try to determine if the file is unrecoverable on the disk. Open the file in Explorer and try to copy it to another location.  I know  I told you to to  work from a copy of the file so you have already done this.  I apologize, the steps were written at different times.
   
   If you can copy the file to another location skip to step 9. If not the actual sectors on the disk may be corrupted. If the data is valuable enough to you, there are several labs that can recover files off damaged disks, you can find a lab here: http://www.disasterrecoverygroup.com/ (there are other such services too).
   
   Damaged hard disk file recovery is not for the faint at heart! If you would like to try there are some free tools here: http://www.s2services.com/diskimagingfreeware.htm.  Try Roadkil's Unstoppable Copier and recoverdm. There are several commercial programs you can buy too, one for as little as 40$. A good list is here: http://www.snapfiles.com/shareware/system/swdatarecovery.html, the File Recovery program at the top of the list appears to be the best.
   
   Conversely for a bad floppy, recovery is usually fairly easy.  A list of freeware for recovering from failed floppies is here: http://www.s2services.com/cdzipandfloppyrepair.htm.

8. Try to open any damaged disk recovered file immediately, miracles do happen.

9. If the recovered file won't open or you could copy the file to another location, try to open the file in a more recent version of Excel. As the version numbers increase, their ability to recover corrupt files increases. If this doesn't work or such a version of Excel is not available, see if some other spreadsheet application is and try to open the file in that program.
   
   A hopefully exhaustive list of spreadsheets is here: http://en.wikipedia.org/wiki/List_of_spreadsheets.  Most of the spreadsheets here will have filters to allow the opening of Excel files.  Most commercial spreadsheets will have a free fully functional trial version.

10. If Microsoft can't help you and you've exhausted all the free methods above for damaged disk recovered or copy-able files there are a number of excellent commercial applications which will recover your files almost immediately. I have used most of the programs in the list and frankly don't like to say anything bad about any of them because somebody is making a living from them. However as they say in this business "Try before your buy!" Always try the free demos first.
    
    Broadly speaking Excel Workbook Rebuilder, RecoverMyFiles, XLS Regenerator and FinalData Premium are more labor intensive and don't have the intuitive turnkey features.

    The others four may do roughly equivalent jobs, although EasyRecovery File Repair at $299 is an investment for future corrupt documents of the Word, Access, PowerPoint, Outlook and Zip variety as it will recover all these if you need it.

    ExcelFix and ExcelRecovery are solid. Advanced Excel Repair, Stellar Excel Recovery, R-Excel, Kernal Excel Recovery and Repair My Excel are newish but appear professional and are lower priced than the pioneers made by Cimaware (ExcelFix), Recoveronix (ExcelRecovery) and Ontrack (Easy Recovery File Repair).

    1. I believe ExcelFIX is the best. A demo is available which will show your first 300 cells. For $89 you can recover data, and for $149 you can recover formats. It's available here: http://www.excelfix.com/.

    2. Another excellent program, is ExcelRecovery. It also cost $149 (with a $30 discount available if you link to their site) and recovers formatting. The Demo version allows you to save 300 cells whereas ExcelFIX only displays them. The company that makes the product Recoveronix along with Ontrack and ExcelFix' Cimaware are the big names in corrupt file recovery. It is available here: http://www.officerecovery.com/.

    3. Advanced Excel Repair (AER) - is relatively new (5 years old, yikes how long have I been doing this?). I have not used it as of yet, but the Web site is quite slick. It supports batch recovery and is relatively cheap for this kind of thing at $89. See : http://www.datanumen.com/products.htm.

    4. Stellar Excel Recovery - "Excel Recovery Software is designed to recover and repair corrupted Microsoft Excel documents. This advanced Excel spreadsheet repair program restores damaged Excel xls files after instances of virus attacks, unexpected system shutdown, media read error, and so on."  Newish too, I have not tried it.  $69.

    5. R-Excel - "R-Excel is a tool designed to recover corrupted Microsoft Excel Sheets. New improvements of file reconstruction technology IntelligentRebuild allow the users to reconstruct damaged *.xls files and to restore lost Excel sheets quickly and easily. R-Excel safely performs any operation, including Microsoft Excel sheet recovery and never deletes from disk, writes to, or modifies in any way, the original Excel files." $79.  I think their other products are great, so this one should be too. Haven't tried it yet. Try the demo.

    6. Kernel Excel Recovery - "Excel Fix software fix & repair excel file that gets corrupted or damaged. Kernel Excel Recovery is an excel fix tool to repair corrupt excel files created using MS Excel 2003, Excel XP, Excel 2000, Excel 97, Excel 95 that fails to open due to virus attacks, unexpected system shutdown etc." Starts at $49.

    7. Repair My Excel - "Repair Excel files with Repair My Excel Microsoft Excel Recovery Software that will: Repair corrupted excel files Repair damaged excel files Repair Excel files from all versions of Microsoft Excel including 95, 97, 2000, XP, and 2003. Repair Excel errors like: "Unable to read file" "The document is corrupt and cannot be opened ..." Have not tried it.  Slick advert - $69.

    8. EasyRecovery FileRepair v6.0 - is an excellent program which repairs all Office files including Outlook (pst) and Outlook Express (dbx and mbx) files. It also repairs corrupt zip files. It is relatively cheap for a suite of recovery programs: $299 but expensive if you are just fixing Excel files. It's available here: http://www.ontrack.com/datarecovery/servicequote.asp.  Hint: use the menu on the left to get to the programs Ontrack has available.

    9. Excel workbook Rebuilder - this is the cheapest at about $30. I have not used it extensively but the new version has 4 different engines for recovering data, which is impressive. This program is really comprehensive with many expert features (VBA stuff), and maybe written for them. I can't tell you how good the program is because I haven't used it that much yet.

    10. RecoverMyFiles - This program works differently then any of the others. It basically scours your hard drive for files and file fragments of a specified file type. Hopefully an uncorrupted previous file or file fragments still exists somewhere on your drive allowing you to recover or piece together your document.  

    11. XLS Regenerator - is similar to RecoverMyFiles, but cheaper program but is just for Excel.

    12. FinalData Enterprise 2.0 (FinalData Premium 2.0) – is a tour de force application, that really concentrates more on deleted file, formatted over files and corrupt disk recovery. There are functions that allow you to recover Corrupt Word, Excel, PowerPoint, MPEG1, MPEG2, and Oracle Export Files if you ask it, but they may not be mature at the moment.
        
        For instance individual elements in PowerPoint (e.g. slides, picture, textboxes etc.) each get a separate file. Each worksheet in an Excel workbook may get the same treatment, I am not sure. If you have other needs and just want your data back in some rough form this may be the program for you. FinalData Enterprise 2.0 is cheap for a suite: $199. The modules are not separable. In addition to the corrupt file recovery abilities and the deleted file recovery it allows the recovery of individually deleted Outlook Express, Outlook Express 4.x, Netscape Mail and Eudora Mail E-mails.
        

11. If these programs don't work to your satisfaction then your file is certainly corrupt, but don't despair there are professional Excel file recovery services or labs. They generally cost $49 and up per incident. Here are some:

    1. http://www.exapp.com/services/excel/ - $99 flat fee with a 2-4 day turnaround time.

    2. http://www.excelwordrecovery.com/ - $50 -$800.

    3. http://www.repair-excel.com/ - Australian firm looks good. Don't know prices.

    4. http://www.excel-rescue.com/ - Cimadevilla Electronica S.L. - Cimaware's parent company has an automatic cheap service costing $50 per file.

    5. http://www.repairfiles.com/index.php - cheap service at $25 - 40. This guy seems to know what he is doing. He is the only one who explains his methods. Impressive explanation of Excel file structure.

    6. http://www.ontrack.com - Ontrack has a service too. Click on the link on the left or on the button to start the easy quote process.

    7. http://www.s2services.com/ - this my service.  I do this for $22.

12. If you don't want to pay the money and you are adventurous, go into Explorer locate the file again, rename the file with a .txt extension instead of an .xls extension. Try opening the file, and if Windows says it can't open it Notepad but will open it in WordPad, agree. Be sure to turn on word wrapping in either program, in Notepad it's under the Format menu; in WordPad it's under the View menu, choose Options, choose the Text Tab, and choose Wrap to window. Next look for where your data stops, and is followed by a bunch of spacer characters they are little squares. These actually begin to tell Excel where cells, columns and rows are. When you find your last bit of data, delete the rest of the file. After this rename it back to an .xls extension, try opening the file in the oldest version of a spreadsheet you can find, or one of the freeware spreadsheets programs mentioned in Step 9. You may be able to recover your data in some semblance of a spreadsheet.

13. Finally if all else has failed, and you don't want to spend the money, you can use a freeware program to recover your text strings and figures (the figure recovery is theoretical) using a Text Extractor.
    
    a. BinText is definitely free but powerful. .
    
    b. TextExtract is another one.
    
    c. Readtext is a third.