my laptop dell d600 says no primary hard disk and when i reboot and press F2 for setup sometimes it shows the size of the hard disk and most of the time says NONE. the pc doesnt detect the hard disk and it sounds like the head of the hard disk is halted trying to read but it fails...I tried the diagnostic tests and it failed in DST short test i dont know what DST stands for but it is related to the hard disk... any help on this?