It seems highly likely that the file is corrupted then. We hear your story several times a year, where a system crash midway through saving a Photoshop file, corrupts the file in a non recoverable way. There are PSD repair utilities out there, but they seldom work, but I guess you have nothing to lose.
FWI, after seeing this happen so often, I increment the file name and save, at least once an hour when working on big projects.
BTW The daftest story I can remember was a poster who was working on a laptop on battery power. He said he knew the battery was getting low, but didn't want to stop what he was doing to plug the power supply in. He ignored several warnings before even taking the time to save the document, and of course, the laptop died midway through when he eventually did try to save. It was a sort of techno-Darwinism in action, and I wish I'd bookmarked the thread back then.