My pc shuts down randomly...
i installed windows 7 on a new hdd but it keeps shuting down
I wanted to reboot it with a disk on key usb drive & run a memory test but it shuts down
this pc ran OK for more than a year ... & now this...
Often random shut downs (in my experience) specially after the computer has been used for a year or more is due to bad RAM. But before you do anything unplug it all check all the connectors for bad pins or crap that got stuck in them and plug it back in. I don't advise taking ram and PCI cards out if you don't have to (lots of people are too rough and then they break their hardware). So just check SATA IDE and power connections first.
Try replacing the RAM and see if that works for you. There are lots of PC places that sell used RAM. Go buy a cheap small stick (1gb or something) take out your old RAM slap that new one in and see if that fixes it.
Other wise you should check to make sure that your motherboard/PSU are not grounding them selves on the case.
And if that isn't the issue then try reformatting (if you havn't already). And while I'm asking that, did you do a clean install or upgrade?
If the unit is rebooting while you are booting off a thumb drive, it is likely a hardware error. I agree with resetting all of the connections in the computer.It sounds like it may be a motherboard or power supply issue to me. If you have access to another power supply, I would try swapping them out to test as well.
Something else to try is to reset the BIOS to default, save settings and restart, then set priority boot disks and so on in the BIOS, save restart and see if the OS will load and run without shutting down.