Computer shuts off by itself?

[bford2660]

I recently purchased a USED Dell Studio XPs 8000. Pretty much since the first time I tried playing games on it, the monitor will shut off and say no signal, then the PC will either shut off or stay going with he monitor not reading it. The shutting down MOSTLY happens when I play games in fullscreen, however, when in minimized version it doesn't normally do it. I've been all over the internet looking for reasons and fixes but have got nothing that worked so far.
PSU- Coolmaster Bronze GX 450W
Graphics Card- NVidia GeForce GT 220
Processor- Intel(R) Core(TM) i5 CPU 750 @ 2.67[Cores 4] [Logical/Core 1]
RAM-4GB
It is running windows 8.1 but was originally a Windows 7 Home Premium OA
I really hope someone on here can figure out something! Thanks!

 

[Hillybobilly]

How's the cooling on that processor? It sounds like you probably are having overheating issues.
If not, make sure that PSU has enough "wattage" for your GPU.
Check Speccy for CPU temperatures.