Check your cables to your hard drive both the power and IDE cable.
It may also be a bad cable.
I had that happen to me a couple of times. But I am cheap, so I get my regular flat cable and cut them up to make a round cable. After about 5-6 months one of the cables stopped working. I think I knicked the wire when I cut them, taking 5-6 months to fail.
Just a suggestion.
Soyo Dragon Ultra Platinum Edition powered by a P4 3.06GHz w/HT @ 533FSB
ATI Radeon X800Pro 256DDR <---Yeah!!! I finally got it!!!
1024MB PC3200, Creative Audigy LS, 2 x 40GB = 80GB RAID 0
Windows XP Pro, DOOM 3, CS, UT2004, BF1942 RtoR, CNC Generals
Finished Half-Life 2!!!!!!!!!!