BIG problem

[Tony2005]

one of my machines for some reason is being very troublesom, first of all when it boots it can't detect the HDD (thought it was the HDD that was playing up) so i swapped it for another known good one. same thing happened, after mesing about with the bios i finally got it to work, after a format i was installing a few programs again and the computer just restarted for no reason.

when it boot up i got the error message "Primary HDD Error", and it could not longer be detected.

i have no idea what it could be

[Tony2005]

never mind its dead for good (the mobo that is)