most epic, but i agree this is prolly your problem, did it start after you added your new video card? if so id definitely say your psu is your problem
Newegg.com - PC Power & Cooling Silencer PPCS420X 420W ATX12V 80 PLUS Certified Active PFC Power Supply - Power Supplies
%20 off coupon Jansave20 with 20 mir = very cheap!
I'd get this at the very least: Newegg.com - PC Power & Cooling Silencer PPCS500 500W ATX12V / EPS12V SLI Ready CrossFire Ready 80 PLUS Certified Active PFC Power Supply - Power Supplies