GB-P55A-UD4P turning off / restarting

[firemansam87]

Components...

CPU: Intel i5-750 2.66Ghz
MOBO: Gigabyte P55A-UD4P
RAM: Kingston KHX2000C9D3T1K2/4GX Kit (2x2G) DDR3-2000 PC3-16000
GPU: Gigabyte GTX260 Super Overclock GV-N26SO-896I
HDD: Seagate 1GB 7200.12 ST31000528AS
OS: Windows 7 Professional

Basically the computer either restarts or turns off. I change the ratio of the RAM and CPU freq and sometimes it will last a few minutes, or a number of hours. But I do not know what exactly is wrong, hardware issue, hardware compatability, software, temperature, BIOS setting...

Does anyone have any suggestions?

[Colorancher]

Check the RAM voltage. I had trouble until I increased the RAM voltage to 1.64. I have OCZ RAM that doesn't register up to its full rated operating voltage and speed.