i built 2 identical computers for my grandparents and one of them keeps randomly locking up and then restarts to bios. i have no idea what the problem is. anyone have a clue or can you tell me what to check. right before it crashes the hdd led comes on and is almost solid and it locks up then crashes and restarts to bios. then i turn the power supply off and back on then restart the computer and all is good. it also seems like the bad computer is not as fast as the one that runs good. here's a list of the componets

biostar atx am2 motherboard
amd phenom 2.3
4gig ddr2
seagate 500gb hd
420w power supply

i can get more detailed if need be.

Need to know error codes.

Based on what you posted, the first thing that comes to my mind would be RAM. Hard drive light makes me think the memory is dumping. Speed is directly related to RAM. (in most cases)

Swap the ram chips and see if the problem follows to the other computer. Quick, free and easy to check...

How long does it run before it craters?

The good thing is you have two identical machines. You can swap components one at a time and isolate any hardware problem.

If you swap the hardware and the symptoms remain, reload the OS.

Blue screen error code?

x2, should be pretty straight forward.

My guess would have been a faulty power supply. Go into the BIOS and check the "power" section, where it shows you your current voltage levels. Make sure they are all where they should be.

sometimes it runs fine (slower than the other one though) for days on end and doesnt crash. i dont have the computer right now. its at my grandparents and im picking it up monday. i forgot to say i already plugged the hd in to a different slot and no help so i dont think its the mobo. ill try the stuff yall said when i get the computer on monday. thanks for the input.

Tell your grandpa to quit looking at pr0n