That would be your PSU as it low quality and its most likely starting to fail now.
You should be running this
Corsair 650w (same price as Corsair 550w)
$100
after rebate $80
http://www.newegg.com/Product/Produc...82E16817139005
This should fix it instantly
I'll give a quick comparison of the Corsair 550w to the BFG 550w PSU
BFG
http://www.bfgtech.com/bfgr550wgspsu.aspx
Corsair
http://www.newegg.com/Product/Produc...82E16817139004
BFG 550w
- 80%+ efficiency
- temperature rated at 25C for stability
- 2 x 12v rails at 18amps each = 36amps (doesn't add up perfectly like that usually)
Corsair 550w
- 80% + efficiency
- temperature rated at 50C for stability
- one 12v rail @ 41amps
Those are some of the main things to look at