Some motherboards have Windows based overclocking programs, but there are no checkmark options in Windows somewhere that you could accidentally enable to overclock. I'm not sure exactly when the Windows overclocking programs started showing up, but I think since your computer is more than a couple years old it is unlikely that would be an option.

Other than the CPU / motherboard / video card / power supply slowly dying, or serious problems with Windows....

Has your computer been either louder or quieter than normal lately? A dying fan could cause overheating, which can cause freezing or reboots. Depending on wether your CPU has any kind of thermal protection built in, it could be throttling down due to heat.

A loose cable or card can cause intermittent freezes or reboots (though not the CPU spikes, AFAIK).


Does the computer seem to work fine for awhile after you reboot, or when you first turn it on, but then start to have problems the longer it is on?

Are the problems worse when you have multiple programs running, etc?

There are probably some diagnostic programs around you could use to try to test various system components. I have not used anything recently, so don't know what to recommend.

...

Randomly trying stuff may identify and fix the problem, but at this point I think it would probably be easier to change the software (Linux or a clean install of Windows) or (if possible) start changing hardware (if you have a spare video card, or can swap with another system, that would probably be the easiest hardware to check, next to RAM).


Also, you might want to make a backup, if you have not done so lately. Even if it is a software problem, you don't want to loose your data (email, saved games, etc) if Windows deteriorates to the point of not being able to boot.