Damnit! HDD got lost out of nowhere!

Well... Ive been accustumed to leave my intel machine on 24/7. And from a while back I had been having troubles with one of my HDD's. From time to time, it wouldn't let itself be detected. So anyways.. my pc was on.. I came back to it a few days later.. only to find it TOTALLY frozen.. and a weird message on the bottom right saying... "File corruption detected, "K:\volume information" has been corrupted, all your data is gone" or something along the lines of that. I thought to myself.. "w t f?" Restarted... HDD detected fine in BIOS... came up to windows.. and no K drive :(. Went into disk management, and there it was.... 40gb's of unallocated space... AAARRRGGGHHHH!!! Ive tried software to try and rebuild the partion... but nothing is working :(. I figured that maybe since it was a freakin accident, it might be fixable, but no... aww shucks. I lost alot of crap in that drive... but nothing that isnt replaceable I guess. Im thinking the drive probably failed during windows usage (its never done that before). Ah well... has anyone encountered a problem like this before?