Oscillating CPU usage

[abogue]

I am running Windows XP on a Compaq desktop w/ wireless
network and cable modem. About an hour after boot up the
computer slows way down. Looking at the Windows Task
Manager, the CPU usage is oscillating between 100 and
about 30. Looking at "Processes", the CPU is oscillating
between System and System idle process. I have run
antivirus and anti spy detection software but it doesn't
help. Rebooting will usually help for a hour or two, but
it always comes back. I had the problem initially w/ Win
95 so upgraded to XP, but didn't help. Any suggestions?

 

[Chad A. Smith]

You might check to see if some scheduled task is trying to run.
Start-Control Panel-Scheduled Tasks.

 

[Arlie Bogue]

I don't see any. I have booted up in diagnostic mode and
it still happens. It doesn't start up at first, when I
boot up the CPU usage is less than 10%. This last time I
let it sit with nothing else running, in diagnostic mode.
The CPU usagae continued to increase, oscillating with
about a 30 second period, until after several hours it was
oscillating between 100 and 30.