PSU Causes Random Reboot

[tpacyga]

I installed a 400 watt PSU, going from a 300 watt. I booted everything fine then 1 minute later it restarts. The next time it happened it totally shuts off and I can't turn it back on, so I put the old PSU back in. Why does my PC randomly reboot like that with the 400 watt PSU? I need the 400 watt PSU, because my video card recommends a 350 watt PSU. Thanks.

EDIT: Oh, I just noticed I put this in the wrong section. If there is a way to move it please tell me.

 

[slick_tech15]

What kind of 400 watt psu is it?

 

[tpacyga]

It is a Rosewill PSU. It was my friends and it worked fine for him.

 

[C0RR0SIVE]

Probably not enough amps on a certain rail and that rail dips low enough that the PSU won't turn on...