Computer shuts down while playing

[advancedbr]

I recently upgraded my computer, it runs fine until I try to play ANY kind of game, I tried GTA IV, FABLE III, Black OPS, and the computer shuts down by itself, sometimes it takes longer to happen, but it always does.

my specs are:

Windows: Windows 7 Ultimate Edition (64-bit) Service Pack 1 (Build 7601)
Memory (RAM): 8184 MB
CPU Info: Intel(R) Core(TM) i7 CPU 870 @ 2.93GHz
CPU Speed: 2930,0 MHz
Display Adapters: AMD Radeon HD 6800 Series | AMD Radeon HD 6800 Series | AMD Radeon HD 6800 Series | RDPDD Chained DD | RDP Encoder Mirror Driver | RDP Reflector Display Driver
Screen Resolution: 1920 X 1080 - 32 bit
Network: Network Present
Network Adapters: Realtek PCIe GBE Family Controller
CD / DVD Drives: E: HL-DT-STDVDRAM GSA-H10A
Ports: COM1 NOT Present
Mouse: 5 Button Wheel Mouse Present
Hard Disks: C: 78,0GB | D: 36,4GB | F: 298,1GB | G: 931,5GB
USB Controllers: 2 host controllers.
Manufacturer: American Megatrends Inc.
Product Make: TP55
BIOS Info : AT/AT COMPATIBLE | 12/14/09 | ACRSYS - 20091214
Motherboard: BIOSTAR Group TP55
Power Supply: Cooler Master Extreme Power Plus 550W

 

[Tmagic650]

3 video cards and a low-end 550 watt power supply don't mix. Try installing a better 650 watt or higher power supply

 

[advancedbr]

actually I dopn't have 3 video cards, I don't know why the program put 3 adpater for me.
I only own 1 video card that is a XFX ATI Radeon HD 6850 1GB DDR5
sry for the bad info
what about now?
is it still my Power supply?
because recently I was testing the heat on my processor, when I'm gaming it hits up to 88Cº, but now the PC doesn't shuts down, because when I'm monitoring my game I leave 2 programs running, "Green Power Utility" that came with my motherboard which gives me the info on Temp, Fan speed, etc... oc the CPU and the "GPU-Z" that gives info on my Video card, If I play withou these programs on the background the computer shuts down after a while playing, if I open the 'Green Power Utility' it doesn't, I don't know if the program controls the temperature better or what.

Also I should tell you that when I installed the Processor, I used the Thermal paste that came already on the Processor, I already bought a Silver based one, but I still haven't put it, since I was doing temperature tests.

 

[Tmagic650]

Remove the "Green Power Utility". It could be limiting the power to your video card, causing the BSOD's

 

[advancedbr]

but it's the 'Green power utility' that doesn't let my computer shut down, without it the game shuts down radomly, so I was wondering if my problem is processor overheating or insufficient power from the power supply. The wattage of my whole pc sums 455W with the 15% watt for secure using, that's why I'm using a 550W PSU