New PC keeps getting errors

[PCNightmare]

Hi

I recently purchased a new PC and installed Windows 7 Ultimate x64 SP1 on the system, and for the first few days the PC worked fine. However recently the PC started freezing up at random intervals, and whenever I start the PC the monitor, keyboard and mouse remain unresponsive, while the rest of the system seems to start up. The system also shuts itself down automatically whenever I start it up, only to start itself up again after a few seconds. Please note that this last error only occurs when I overclock the PC, however this should not be a problem as my CPU is 'supposed' to be able to overclock. Any help anyone can give me would greatly be appreciated as I am missing out on some serious gaming time! The specs for my PC are as follows:
Intel Core i7-2600K (3.4GHz, 8M Cache, 8x Cores) Overclocked to 4.6GHz Per Core CPU
ASUS P8P67 Pro (B3) P67 LGA 1155 SATA 6Gb/s USB 3.0 Motherboard
NVIDIA GeForce GTX 580 3GB 384bit DDR5 DX11 Graphics Card
Antec DarkFleet DF-85 USB Gaming Case
Antec TruePower Quattro 850W 80+ Modular Gaming Power Supply
8GB DDR3 1600MHz High Performance Gaming RAM With Heat Spreader
Two Storage Drives
OCZ Agility 60GB SSD Read: 525MB/s Write:475MB/s SATA3 Solid State Drive (OS Drive)
1TB Western Digital Caviar Black 7200RPM 64MB Cache SATA3 6.0Gb/s Hard Drive (Data Drive)
24x Dual Layer DVD +/- Writer
Noctua NH-D14 Dual Radiator 6 Heatpipe with 140mm/120mm Dual SSO Bearing Fans CPU Cooler
Integrated 8 CH High Defination Sound Card
Integrated Gigabit LAN Card - Broadband Ready

 

[oboedad55]

I am no overclocking expert, but is it perhaps a heat issue? Do you have sufficient cooling for overclocking the CPU

 

[scrooge]

i'd say heat trouble aswell download (realtemp) and see how hot your running your rig at.

scrooge

 

[PCNightmare]

I doubt it's heating trouble(my CPU never goes over 40 degrees C) but if anyone has a way to verify that it isn't heat it would be greatly appreciated. My system has also started giving me a new problem: It bombs out at random intervals and loses all power, causing me to lose everything I have been working on

 

[oboedad55]

Power supply? I just replaced one that was giving me weird, random problems until it just croacked.