Why does my computer video skip? Video card problems?

I have a Dell XPS 420. I updated the video card to an Nvidia, I believe the Geforce 9800 GT. After installing, I didn't seem to notice any problems, but I've found myself having some computer issues that I didn't have. For example, my Presonus Firebox will loose it's connection when I am watching a video, or watching Slingbox. Or watching a video will sometimes skip, or make pop noises. Not a lot, but enough. I updated the drivers on my video card & sound card. Not sure what might be the problem? It's still a fast computer, and I love it. Just want it at it's peak. The sound card thing is really annoying too. Its hooked up firewire, so I have to disconnect & reconnect to get the sound back on.|||it is an internet connection issue