Homebuild dies but hours later works again

[lemmoncake]

i have had alot of problems with my home build i got it in September. psu died November. got a new one plugged it in day later gpu died thats due to arrive back next week however for the last 3 days i have had 3 crashes computer just turns off and wont power up for hours then when turned on works fine till the next crash. has happend 3 times so far from hours of working to just after start up. i thought maybe the cpu was overheating used a program to check it 29-36 degrees so unlikely to be that. i dont have a second computer to check this on which kind of limits my diagnostic build is as follows! HELP!!!!

Mobo:
ASRock Z77 Extreme 4, Intel Z77, S 1155, DDR3, SATA III - 6Gb/s, SATA RAID, PCIe 3.0 (x16), D-Sub/ DVI-D/ HDMI, ATX

Cooling:
Cooler Master Hyper 212 EVO, 4 Heat Pipes Direct Contact, with 120mm Quiet Fan LGA775/1155/1156/1366/AM2/AM2+/AM3/FM1

Graphics card:
3GB XFX Radeon HD 7950 Double D, Black, Ghost/HCell, 5500MHz GDDR5, 900MHz, 1792 Cores, HDMI/mini DP+

Screen:
Acer S230HLBbd DVI LED Full HD DVI/VGA 1920x1080 250cd/m2 100M:1 5ms Black

RAM:
8GB (2x4GB) Corsair DDR3 Vengeance Low Profile Cerulean Blue, PC3-12800 (1600), CAS 9-9-9-24, XMP, 1.5V

DVD Drive:
Samsung SH-118AB/BEBE Black 18x SATA DVD ROM - OEM

PSU:
550W xfx pro

OS:
Microsoft Windows 7 Home Premium 64 Bit SP1, Operating System, Single, - OEM

Hard drive:
3TB Seagate ST3000DM001 Barracuda 7200.14 SATA III 6GB/s 7200rpm 64MB Cache 8ms NCQ OEM

CPU:
Intel 3rd Generation Core i5-3570K CPU (4 x 3.40GHz, Ivy Bridge, Socket 1155, 6Mb L3 Cache, Intel Turbo Boost Technology 2.0)

Case:
Coolermaster Storm Enforcer Mid Tower ATX Case

 

[Outlander_04]

turns off like someone pulled the plug out of the wall socket?

You have a power supply problem . And since its happened b4 you may have problems with the wiring behind the wall socket causing volateg spikes and killing the psu .

try it plugged in somewhere else