PSU affecting Graphics Card?

Hi guys,

Hope someone can help me answer this question..

I've just rebuilt a new PC, Q6600 + Asus P5KC + Sapphire 4850 Dual slot cooler...

I'm pretty sure my PSU is faulty, whenever i plug in pen drives, it locks up err kind of normal routine

my question is, will/can a faulty power supply affect my graphic gaming performance? playing gears of war i seem to get quite glitchy graphics, hard to explain but when i move the mouse up and down lately it seems to pick a horizontal sectin and almost freeze for a second, im not really sure if it's classed as lag but that kind of thing..

Also, when i run ATITool artifact scanner because i did have my card o/c'ed i thought i might have messed it up, no artifacts found after hours of scannin but when it is scanning my display has faint scrolling horizontal lines coming down it? is that a normal procedure when its testing or not?

so guys... whats faulty in my system? graphics card or is it as i think PSU??

Thanks in advance!
Alex