My laptop periodically would start running full speed, with the fan whirring loudly and Task Manager showing 50-60% of CPU time being using, even when no tasks were running. It took me a while to figure out what was happening.
Norton Internet Security was hogging processor time. With a few tweaks, I fixed the problem. Here’s how I did it (in Vista.) Other security programs can have similar problems, so maybe this can help you too.
Close all applications. Start Task Manger with ctrl-alt-del, click Performance tab, click Resource Monitor, click CPU. It will list what’s running and more importantly, how much CPU time each process uses. If one process is hogging large amounts of time, then that’s the culprit. This is where I discovered Norton was hogging 40% of CPU time.
I went to the Norton Internet Security main screen and discovered the CPU Usage info on the left tells you how much CPU time is in use and crucially, how much of that time is used by Norton. You can optimize Norton by clicking Norton Insight under CPU Usage. It will scan your system and mark files that are safe and thus never need scanning.I also changed Settings / Miscellaneous Settings Idle Timeout to 20 minutes from 10 minutes. Once I did this, the problem with my PC racing went away.