Comp Random Shut Down

My computer randomly shuts down no BSOD, and pretty sure its not an over heat, happens more often during gameplay, but still happens at idle, or web browsing, and reg usage. The only thing that shows up when turned back on is "Windows did not shut down properly" and a kernal error. It'll straight shut off no warning or message, and can be turned right back on instantly after the shut off. I've ran hdd tests, and ram test and re-installed video and chipset drivers, and it'll still randomly shut down. It runs BF3 for about 30-90 min before a shut down, and WoW or idle almost with no set average time that it occurs, but still happens.

System specs are:

Thermaltake Element G case
MSI NF750-G55 mobo
AMD Phenom II X6 1055t @2.8 GHz and 3.3GHz OC (OC was set back to stock speeds no change)
AMD Radeon HD 6770 / XFX (no OC)
2x2Gb Patriot RAM 1333MHz / 2x2Gb Gskill 1600MHz down to 1333 / 8Gb total @ 1333MHz
Zalman CNPS 9900Max
250Gb Seagate HDD (tested with seatools)
500 watt Raidmax PSU, came with a Raidmax Smilodon case
Windows 7 Professional 64 bit

*the case fans and cpu fan keeps the system quite cool and temps while under load dont seem dangerous.

All drivers were reinstalled and problem still occurs, and my next step would be to reinstall windows, but if anyone knows wat might be causing this before I start individually testing and switching out mobo/cpu/gpu/psu and singling out wat the issue is I'd appreciate it.
 
Solution
Most likely the power supply couldn't survive the load from overclocking. I had the same thing happen to me with a low grade ps. I recommend antec, ocz, and corsair for value and performance. Look for 35-40 amps rating on the 12v rail.
Most likely the power supply couldn't survive the load from overclocking. I had the same thing happen to me with a low grade ps. I recommend antec, ocz, and corsair for value and performance. Look for 35-40 amps rating on the 12v rail.
 
Solution
found out that the two different speeds of 1600MHz and 1333MHz even when down speed all at 1333MHz RAM i was using was causing the problem, took out 4gb and test both separately, and both 4gb of ram worked perfectly fine and played bf3 for hrs with no shut down, ordered new 8gb 2x4gb Kingston HyperX blu @1600MHz to get rid of using only 4gb!!!! when u get use to using 8gb, u really notice the difference.