Joseph makes a good point, except the fact that if this were so, your processor would heat up quickly and your computer would occassionally reboot without warning. If you believe this is a heat issue you could always take your computer in for a professional cleaning, or you could buy some air cans and do it yourself. If you have no idea how to clean a processor, I would advise you not to bother with it.
If you were running out of free disk space you would recieve a warning constantly from your operating system.
What is the model number of your pc?
If it were a power supply fan, then your system "would" more than likely continue to run, though I am not sure how bad it would bog your performance, it depends on how many fans you have in your unit.
I would suggest downloading new video and audio drivers, it is possible that these may have corrupted.