PSD file can be opened in Illustrator and even acrobats. On Photoshop in this case is usually the most loyal. Even the previous version opens the file later version (though I do not know about CS5). Therefore, if you have Photoshop CS5
does not open the PSD, made in CS5, and if an acrobat and illustrator also did not open, then, alas, the file is actually damaged.
I would in your place, took advantage of this program:
http://www.photoshop.recoverytoolbox.com/
Also you can find more information about your problem here:
http://www.filerepairforum.com/forum/adobe/adobe-aa/photoshop/207-can-t-open-a-psd-file-through-photoshop