Computer randomly powers off

Penfold29

Honorable
Mar 20, 2013
7
0
10,510
I have just upgraded my CPU and processor, and now randomly my computer just powers down (like a power failure except the PSU still has power)
I have been monitoring my temperatures and they are fine)
It's weird because I can run something resource heavy like Battlefield 3 on full graphic settings with no issue but then I can be just browsing the Internet and it will suddenly fail.

Interestingly the only way I can make it fail every time is to run the windows experience assessment test (where it rates several components between 1.0 and 7.9)
It gets through all the tests but just before completing the final test "assessing disc performance" the system powers down every time


For info I am running
Windows 7 Home Premium 64 bit
AMD FX 8350 Processor
As rock 990FX extreme3 Motherboard
16gb Patriot G2 RAM
Nvidia GTX 460 Graphic Card
Samsung SSD 830 256 GB Primary HD
Power cool 950 watt PSU

What could this be?

Jake