slowed way down - not a virus problem

[turbo24]

I am running XP Pro at home, and I have noticed a HUGE slow down on my computer - particularly on internet.
I know what the first thing you think of is virus or spyware, something along those lines. However I have scanned for both and used different sources to run the scans just to be sure. I connect thru cable modem and I also have my sisters laptop and my secondary computer sharing that net connection and neither one of those are having these issues.
Heres the part where audio comes in. The net runs basically okay till I try to listen to any type of audio file. Like for example a sample clip of something. The file types I have tried to listen to have varied and so have the "players" that have been trying to play them. But theh audio will not open and once I have tried the one time to open an audio sound clip, my whole internet just crawls slower than dial up even. I cannot figure out what the heck is happening.
Any ideas?