error on photoshop cs4 at opening file

I've been working on a photoshop file all week in CS4. Today I go to open it and it says, "Could not complete your request because it is not a valid Photoshop document." What!? I did nothing to save it different from usual. I've tried copying the file, renaming the copy, using a different file extension on the copy, etc and nothing will work. I can't redo the file, it was a week's worth of work - help me!!

Please, please, anything you can tell me. I am desperate here!!

If solution on above doesn’t work or your .psd file is severely corrupted, then I would suggest you following ways contained various tips for crashed Photoshop images

https://forums.adobe...message/6698481

http://itknowledgeex...-photoshop-cs6/

https://www.openfile...om/psdopen.html  PSD Open File Tool

·         Open "My Computer" from your desktop. Double-click your hard drive.

·         Open "Documents and Settings."

·         Open the folder labeled with your user name.

·         Open "Local Settings" followed by "Temp."

·         Scroll down to the files beginning with "Photoshop" ("PS" for older Photoshop CS builds). This will be followed by a series of letters and numbers.

·         Double-click each "Photoshop" ("PS") temp file to open them in Photoshop CS. This is the only way to identify which temp file contains the project you wish to recover. Luckily, because when Photoshop shuts properly it deletes its temp files, there should be no more than three or four.

·         Select "Save As" from the "File" menu when you find the temp file you want. This will make the file permanent