Computer Help --Audio & Video Problem

I hope some of you guys and/or gals can help me out. I have tried to fix this problem for a couple days without success. I hope it's not anything major.

OK, here is the deal. Whenever I download a video to play in quick time, real and/or windows media player and try to watch it, my audio keeps cutting out and the video wants to play faster than it is supposed to. When I watch streaming video from places like youtube, I have no problems. Does anyone have an idea as to what the problem could be? I have cleaned my cpu, defragged my hard drive, ran virus scans, updated the audio/video players, tried to find new drivers and have no success.

It's driving me crazy and any help would be greatly appreciated.

On an unrelated note, does anyone know how I can get my internet connection to run faster while hooked up to my router? When I run a speed test, it's showing the same speeds whether connected directly or through the router. Streaming media doesn't run quite as smooth while running through the router.