Computer random crashes and restarts

My computer keeps randomly restarting. It doesn't matter if I'm browsing the Internet or playing games it will just happen randomly. It crashes most frequently during the boot up after the initial crash. system repair will give me a few extra minutes but it eventually crashes again. When rebooting it will turn off and on and ONE of my case fans which is connected to my motherboard will flicker on and off. i have other fans connected to the board that do not do this.
I've never posted here so I'm not sure what I should include in this post but here are my parts.

Motherboard: gigabyte GA-970A-UD3 AM3+ 970 R
Video Card: Radeon HD 7770 1G
Power Supply: Corsair HX750 750W
CPU: AMD Phenom II 3.4G AM3 R
Memory: 4Gx2 Vengeance
Hard Drive: 1TB SATA 6.0 32M
Windows 7 Home edition 64bit

Things I've done:
-booted in safe mode (still crashed and restarted)
-system restore (still crashed but less frequent)
-checked and secured power connections to the mother board
-sysstem repair (same as restore)
-Began a virus scan but computer crashed before it could finish
-checked CPU heat (remains 35-45 degrees Celsius even while playing games)

let me know what information I need to add.