Problem with a computer randomly restarting

[RAF Bomber]

Hae guys one of my computers just randomly restarts while in use.
Sometimes it will do it when it is just booted sometimes it will do it after it has been in use for hours.
It is a Packbell
Intel Celron 2.0Ghz
160 Gb Seagate HD
256MB nVIDA FX5500 AGP card
1256MB RAM
ASUS DVD/CD writer

Sometimes when it reboots is gets the error 0x00000024 for windows, but i am not sure if this help becuz this could have been caused by a number of things

So far i have
Run memtest to check that ram up to 200% no problems
Run seatools to check the hard drive and there is no problems
I have recently added the graphics card, but i also have the same graphics card in one of my other computers and are not experiencing any problems with that

Have you guys got any ideas of what could be causing the problem and a fix for it?
I thought maybe the PSU but idk

Cheers

 

[mpilchfamily]

It could very well be a power issue. The addition of the video card may be maxing out the PSU.

IMO its not worth the cost of the PSU to fix. Unless there is some reason you have to keep this PC and don't have a newer one to use.