My PC is acting strange?

It all started when youtube couldn't run.A black box appeared with no loading whatsoever.I tried solving with downloading the latest graphics driver,ati catalyst 10.xsomething something.In the install wizard it said it couldn't run on windows xp so i stopped the installation thinking that youtube will work again.Not only was youtube not fixed but i had more problems then youtube at that point.Whenever i scroll in an internet browser depending on the direction a white line goes up and down in the direction i scroll. Also,no computer game will run at all.For example Warcraft 3 just crashes.Please help it's getting really annoying -.- thanks in advance :D.Oh and mcafee didn't find any threats on my pc.