PC Powering Off Randomly

[galaga4991]

I just got my new PC all set up, but every 20 min or so, the PC will completely power off. What could possibly be causing this to happen? Here are my PC's specs:

AMD Phenom II X4 955 w/stock cooler
2x2GB (4GB) G.SKILL DDR3 1600 RAM
XFX ATI Radeon HD 5770 1GB
ASUS 790X chipset Mobo w/ DDR3 1800 support
550w OCZ Fatal1ty PSU
Antec 300 case (With 1 120mm fan and 1 140mm fan hooked up to the PSU)

Also, it is hooked up to an outlet which can support up to 20 amps.

 

[idejason]

Please post your motherboard model name.