This answer is for posterity -- I was in a similar situation today and successfully recovered the file.
A .txt file I was composing (in Notepad++, but that's beside the point) became corrupted after a lock-up/system freeze. It was the only file to do this (probably because it was the only one I had open at the time). I use Windows XP. The 14,000-line-file had turned into a bunch of NULs. Windows continued to show the correct file size after the incident.
First thing I did was run chckdisk. AFAIK, it didn't help any. I learned about Recuva. I ran it without installing and let it do its deep scan. But after an hour, it had pulled up only 20 or so "complete" "excellent" files that were previously deleted by me and the one I wanted was not among them. I changed advanced settings--which I should have done first time around--to allow the next scan to search for files that were not deleted. I checked the box next to the filename when it came up in the list and hit "recover". Success!!
I got a few days of my life taken away from me today to stress and worry, but I did learn at least one important thing from my ordeal: to backup frequently!