Computer shuts down during playing games

[glit1]

Hello
Before I start explaining I did not have this problem before I upgraded + im not the best at computers
So I bought a new video card (NVIDIA GTX 560 TI) cause my old card was really bad. So when I started playing I tested the graphics on APB(All Points Bulletin), before I upgraded I would only be able to play on low without lag but now I could play on High. And so after 10 mins or so of playing my computer would just turn off and then on agian after about 5 secs. I started it up agian and put the graphics on low and disabled all the special graphics options + put the fan speed on high. Now I can sometimes play for 2 hours and sometime only 30 mins which is really wierd cause GTX 560 TIis suppose to handle atleast High on a game like APB.
So what I am wondering is what is causing this problem and what can I do to fix it?

Computer Specs:
Computer: HP pavilion m9651me
Processor: Intel(R) Core(TM)2 Quad CPU Q9400 @ 2.66GHz
Video card: NVIDIA GTX 560 TI
Memory:8gb RAM
OS:Vista & SP2
Power supply: 300watts(Not sure how much)

The picture shows the temps of my computer just for sure.

Thanks

 

[Dannyk0ed]

The problem is your power supply, 300 is not enough for gtx 560ti, get 550+, open your case and look at your powersupply,

 

[glit1]

ah thanks getting the Super Flower / AXP Power Supply with 120mm Fan - 650W
soon will it work?

 

[Dannyk0ed]

Wll work good if you install it correctly.

 

[glit1]

Will probably have to leave in to a computer shop
Thanks alot !