I've run Ad-Aware, Spybot and done a virus scan with McAfee and nothing shows up. The high usage is coming from System (about 98 percent) and there's nothing on System Idle Process. I've attached a HijackThis log for reference.
This problem is on a Compaq Presario 2100 laptop and it occurs whether or not I'm using AC or battery power. I am also unable to go into stand by or shut down. The system freezes on the window showing shutdown in progress and I have to shut down using the power button.
To complicate things further, I don't think I can use "repair" on my Windows XP install CD because it's SP1 and I've upgraded to SP2. If need be I'll do a clean reinstall but if anyone has any other suggestions I'd be grateful for any advice.