Just recently I upgraded my PC from WIN98 to WinXP SP2. My regular uses of surfing the net, listening to audio (streaming from the internet or from a CD or watching video clips and burning them onto a CD in VCD format or DVD in DVD format) were runni9ng fine even after the upgrade.

Then a couple of days ago, the audio started crackling, so0unding oley for the most part but with a crack every so often (almost seems like something else was also using the sound card). The video while playing also seems to have a slightly slower refresh rate. When I want to burn the files to CD, the crackling (in the case of audio) and pixelly, blurred, skipping in the case of video is also transferred to disk.

I am using Nero to burn the video to CD as VCDs and using Windows media player to burn the audio to CD.

I thought it might be a virus so I reinstalled XP, but the problem still exists. Whats goin on and how do I fix it?

from what you posted, i would be fairly sure that it is a codec problem. luckily, you will have a suite of em on board to pick and choose from, plus you can troubleshoot them, and if needs must, download new ones from the maker of your audio chipset eg realtek.... , or from microsoft [mediaplayer comes with a set of codecs], or from .... The place to get the basics on this is this website:
http://www.updatexp.com/windows-xp-codecs.html
The codec with priority 1 is the one you are probably having trouble with...try another. anyway, that website, 2/3 down is a link to a free [and it is] codec utility, Sherlock. Try it. Make sure to select audio codec output in the listing!
Oh, and cos this stuff is free, it doesn't hurt to click on a couple of his ads. he gets paid that way..