SLoooOOoooW PC issues

Discovered that my home PC drive is very defragmented. My brother has been complaining about how slow my pc is (Im supposed to be the PC acting as the server for Internet Sharing) which brought me to try and "fix" the situation.

I defragmented my HD first. It was bloody fragmented. I figured a couple of months ago everything seemed fine and running a-ok, so it cant be running out of memory. I barely installed anything since , oh, like whatever. My brother keeps saying im running out of memory, but the diagnostics doesn't seem to think so. So i figured, It could be the file page/swaps....

Afterwards I scanned the disk for bad sectors. Everything, from 10pm, all the way to 2am early this morning, no less.

I've also run the antivirus, several times, to boot.

Now my HD is not fragmented, ... Looks very clean. Added back the page files in again. Doesn't seem like there's any problems that'll crop up now.

Uh-oh. And now my CPU hits 100% when I run an avi file.

EgAd.

I hope I dont end up reinstalling the system from ground up... Its going to be a hell of a weekend if that pushes...