Flashing screen in games

Hi all, the problem is this: in normal operation everything is fine, but when you start the game flashes the screen as if he was a second off, the higher the count the more it is aggravated by blinking. Maybe not enough possibilities of BP? I read that only this vidyuhi more than 100 watts it consumes. But check other PSU there is no way, as friends only even weaker and buy it, too, is not an option, suddenly not in it business. About the temperature of the card - PlayClaw showed 60 degrees. Please tell me. The PC system requirements are:
CPU: QuadCore AMD Athlon II X4 640, 3000 MHz (15 x 200)
RAM: Kingston 4GB DDR3-1333
Video card: NVIDIA GeForce GTX 550 Ti 1Gb
Hard on 1 TB
PSU 450W
Syst. fee: S-Am3 ASUS M4N68T V2
I know that the monitor is okay. And what about a video card and PSU do not know. Can't check them, so don't know what parts to buy.