1Yr old computer - Lag problem

The problem occurs when I either play a game or browse the internet and watch a movie on my other screen. Let's start with the specs.

HAF 932
CPU: Intel Core i7 930 @3.9GHz
MB: EVGA X58 LE Edition SLI (Intel X58 Chipset)
Memory: 6GB DDR3 1600MHz Digital Storm Certified Performance Series
PS: 1200W Digital Storm Certified (Dual/Triple/Quad SLI Compatible)
Main HD: 1x (40GB Solid State (By: Intel) (Model: X-25V Edition)
2nd HD: 1TB
GPU: 1x NVIDIA GeForce GTX 480 1.5GB (Includes PhysX Technology)
Air Stage 1 Cooling Noctua dual fan 120mm

1 24" Asus monitor 1920x1200
1 23" Acer monitor 1920x1080


SO, there's my PC. I have 7-8Gig left on my SSD, everything else is on the second HD.

Now, when I'm on the internet and a movie playing on the smaller screen, whenever i load a page my movie starts lagging and the sound skips - all the time-

Same thing happens when I play game and watch a movie at the same time. I use Windows Media Player - full screen, and my game either in full screen or windowed. 1 of the 2 application is always windowed.

So please help me find what's happening. It wasn't happening before but it is happening for the past month or two.

I'm a little mad because the pc cost a lot of money and I tought it could handle 2 screen easily.


Thanks!

P.S. Anyone can explain to me why there's no HDMI port in the 480GTX??

Tyvm!