I had this once.......I baught my computer from aria, and it came faulty and whathavya anyays it got sent too and fro a few times and I ended up voiding the warranty by going in the case.
I noticed my hdd was plugged in the IDE 3 slot of my board. Thats stange I thought, but left it.
One day my hdd and windowsxp was playing up and did a reformat and partition, I lost 10GB off my disk somehow. Anyway, big do's and little do's I tried the IDE 1 and IDE 2 slots of my board and it found it all staright away, piece of piss.
Might be unique to my system, but you coould try another IDE slot perhaps?
Best see if anyone well up on computers disagrees first though
lol.
See ya
Sirius.