HELP ME! my new computer is crashing and wont even start up.

Ok i just built a new computer and everything was working fine. A few days ago my 5 year old computer started crashing. It goes to the black screen that says windows failed to start properly and it makes me choose a mode to start it in( normal safe etc) Then it just turns off. I didnt think anything of it since the computer is 5 years old. Now the same thing is happening to my computer. When i get to the windows xp loading screen it just turns off. I never even make it to my desktop Please help me. Is this a virus? My power suply is powerful enough.

and it is now happening to both computers. help is much aprreciated

I had the same issue once. Turned out to be a loose connection between the PSU and my power cable. Check all your connections.

Other options:

As you state: You PSU might be underpowered. Post specs, and someone might be able to tell

If you are reusing some peripheral from your old computer, that might be the cause, if the component is defective and shorting out.

i have a q9300, radeon 4870 512 ddr5, 2gigs of ddr3 1333, and a 650watt power supply