Computer Slows Down When Playing ANY Video File?

i have been having a persistent issue that i can't seem to fix. it started when i would watch a video on Internet; any video! i would start to watch a video and within a few minutes, it would start to stick and playback would slow down on the video and anything else i would be doing on my computer, and then even the audio would be filled with static (as if it were a radio station). i was always able to "x" out of Internet, but then i realized any video i watch anyway on the internet would do the same thing, (if it played long enough). sometimes i was able to play a whole video without this issue, but now, it is becoming persistent. sometimes this problem would start a minute after the video commences, other times, it would start 10 minutes later, or 30 minutes later. at this point i have not been able to watch any video file from any site on the www. have run scan after scan, and system says nothing is wrong. last night, i resorted just to listening to audio files (on wmp) and now it is acting up too! (sounds like i have 'bad reception on my music files all of a sudden). i ran the microsoft fixit program last night, and it suggests i should delete some codecs