BIOS doesn't find HD, and computer keeps locking up.

[Alive]

If its not the drive (consider an rma) try and clearing your bios via the jumper on the mother board (some state "bios" or "cmos" next to it) or pull the battery for a minute or two (sometimes works, sometimes dont) is the drive making any peculiar noises at all? (it might be bad) other than all that fun stuff, it could very well be a nasty virus thats maybe attacked your bios (corrupted it) or wigged out that drive of yours...