Actually
So when my movies started working, I tried to load up WoW and had MAJOR tearing/graphic errors.. Wasn't just with WoW either. same thing happened in Guild Wars, EQ2, and WC3.
In the end I got it fixed, turned out it was my power supply unit (PSU).
On the side of your power supply, there is a sticker it will have six plus readings under DC Output. You only need to pay attention to 3 of them. What you are looking for are the ammrage output of the rails. You only need to pay attention to the positive DC Outputs and these are;
+5v, +12v, and +3.3v. These are called rails and you need to pay particular attention to the +12v rating as from what I've learned this is mainly what your sound card, and video card use.
You might have two 12v rails and your sticker would read as +5v,+12v(1), +12v(2), and 3.3v
At any rate, my PSU was rated at 16A(Amps), however, my video card required 20A on the +12v rail.
I got a new PSU, one with dual +12v rails rated at 21 amps each and bam! I could watch videos AND my games ran great!
As a side note, if you get a new PSU, the +12v rails don't add up exactly. From what I was told, you only get 80% of the combined total so in my case, I now have two +12v rails at 21Amps each, so instead of 42, I actually only have 33.6Amps to power my Video card, Sound Card, and CD roms.
Hope that helps. Cuz I know I was sure frustrated having to watch porn on another computer and game on my main computer...