I would try a bunch of stuff before starting over, but I would be willing to bet that you will have to start over.
If you are double clicking on the file, try something else by going into Photoshop first and then selecting the "Open" command, navigate to your file and try to open it from there.
If that doesn't work, try placing it into InDesign. If it places in, then you should be able to work with it somehow.
Try different computers, try classic Mac, OSX Mac, try changing the name at the end to be ".psd", try copying it and trying to open that copy, try burning it to CD and seeing if you can open it up off of the CD, try a PC if you have one, try an older version of Photoshop.
Just a few options, try anything you can think of and if none of that works, then go back to the drawing board and start over.
We've all been there, so don't feel too bad.
