Computer shutdowns

[y2k45]

My computer i built my self, is shutting down during gaming. I have built computers before and they worked flawlessly.
This issue stumps me.
My cpu/gpu is not overheating, temps are around 50celcius.
I stress tested my computer, it passed all tests. tested ram, ram is fine. Video card has been stress tested, it is fine. I am coming to a conclusion it may be my power supply dieing.
The PSU i bought in 05 i think , im not sure.

my setup is.

Motherboard : z68A-D3H-B3 intel motherboard from gigabyte.
Video card: gtx 460 1gb
CPU : intel core i5 2500 sandy bridge 3.3ghz
RAM: RipJaws DDR3 1600 9-9-9-24 X8 gb
harddrive:Western Digital Caviar Black WD7502AAEX 750GB 7200 RPM 64MB Cache SATA 6.0Gb/s 3.5" Internal Hard Drive -Bare Drive
PSU: OCZ gaming extreme 700W
I am completely stumpped but have a good feeling its psu dieing

 

[christop]

Do you have another psu to try and see if that fixes the problem.

 

[y2k45]

I am going to order a 1000W psu and test, i dont have a spare.. it is frustrating, it happens even when you just start a game.. blam shutsdown

 

[y2k45]

hmm, now it wont even load properly, shutsdown during post too! omfg, im at a loss for words what could be doing this. i took out and tryed individual sticks of memory, a new harddrive, no deal??...