SATA1 HDD's sucks man!
I had the same problem, and a friend of mine who had the same problem too!
One day, the computer worked fine, the next day the BIOS did detected the HDD, but It doens't appear on the Windows drives list, neither in Windows Device manager... Like I said, this seems to be a SATA1 usual problem.
I never heard anyone having any problems like this with SATA2 HDD's though, and I hope I never do, coz I just bought a 320gb SATA2
There are ALOT of programs to recover data, maybe too much of them... maybe because none of them fucking work... correctly! Still, if you wanna give it a shot, I uploaded some file/hdd recover apps's, here, have fun... :roll: