Really Slow XP

Hello,

In the last week everything in Windows has ground to a halt, it has been fine for years but has all of a sudden decided to stop working!!
I have taken the usual steps, ran a full system anti-virus scan, no problems, ran SpyBot, no problems, copied loads of media files onto an external drive and deleted from the computer, defraged the hard drive, ran a registry check, fixed the problems and defraged the registry - all with no improvments.

What I have noticed is that the CPU usage meter in Task Manager is running at 98% to 100% when I am not even doing anything!! Previously it would be around 35%, is this a hardware problem or something wrong with windows?

p.s. By "ground to a halt" I mean that it is taking a very long time from clicking on something for it to open, the mouse freezes when you drag it and then starts working again, when I open AOL I have a womans voice saying "Welcome To AOL" but know it sounds like "wellllllcome to aaaaaolllllllllll", if you see what I mean!!