Computer keeps shuting dowm !!!!

[mach1korea]

The computer keeps shutting down even in the bios screen, it will boot to windows 8 but I have been pressing delete to get to setup rather than keep crashing windows.
I have disconnected everything except video card Evga 650SC and boot ssd transcend 128gb. I have a FX8120 cpu and wixx 600 watt psu.
When I power on it posts and i can get into the bios screen, everything appears to be Ok and then it will shut down. If I then wait 2mins I can then reboot and get into bios. The same thing happens, the longer I leave it switched off the longer it is before shutting down but no more than 2-3 mins before shutting down.
Ok, I think the power supply has died does anyone else have an thoughts?
If it is psu what size wattage and make would you recommend?
Thanks

[wazza300]

could be psu,corsair/seasonic/xfx are good brands of power supply

other thing to try is try with only one ram stick installed and see if its more stable