Computer Random Restarts

[popius]

Recently I have been experiencing random restarts with my computer. It is not even 2 months old and has been good for the first month. Everytime I boot up the PC it will randomly restart after about 5 to 15 minutes. Once it loads back up it will restart again maybe after 10 minutes. It seems after it restarts after 2 or 3 times it is ok and will run for a few hours.
I have tried booting up in safe mode and it still restarts. I also tried reformatting everything. While the reformatting, the computer restarted. This happened twice, while reformatting and during the installation of the OS. Could this be a problem with the CPU overheating? I'm using the stock heatsink. Sometimes when the PC restarts, it takes a while to power up again. Maybe about 2 minutes, even when I try pressing the power button.

Anyone have any ideas?
Thanks


This is my build

Corsair Professional HX750W 750W ATX 12V 62A 24PIN ATX Modular Power Supply Active PFC 140MM Fan
Gigabyte GeForce GTX 460 Fermi 715MHZ 1GB GDDR5 2XDVI Mini-HDMI PCI-E DX11 Video Card
ASUS P7P55D-E Pro LGA1156 P55 DDR3 2PCI-E16 3PCI-E1 2PCI SLI CrossFireX USB3.0 SATA 6GB Motherboard
Western Digital Caviar Black 1TB SATA3 6GB/S 7200RPM 64MB Cache 3.5IN Dual Proc Hard Drive OEM
Intel Core i5 760 Quad Core Processor Lynnfield LGA1156 2.8GHZ 8MB Cache Retail Box
Samsung SH-S223C 22X DVD Writer SATA Black OEM
G.SKILL F3-12800CL9D-4GBRL Ripjaws PC3-12800 4GB 2X2GB DDR3-1600 CL9-9-9-24 Core i5 1.5V Memory Kit
Coolermaster CM 690 II Basic ATX Mid Tower Case Black 4X5.25 6X3.5INT Front USB eSATA Audio *No PSU*

 

[ulysses35]

1 = PSU - random re-boots could be a weak or defective PSU - if the unit is still under warranty then you can RMA it

2 = CPU HSF - quite a common thing to get wrong - incorrecty seated HSF's can cause overheating - this would possibly explai nthe re-boots and sluggish perforance. modern CPU's are design to throttle down if they over heat.... worst case scenario the pc shuts down. if you take the side panel off and touch the HSF and it feels very hot afte a few minutes of use then try re-seating the HSF. I presume the fan is the stock intel item ? the push pin design is rubbish and its VERY easy to think you have them locked in place and then assemble the pc with one pin not secured.