[King Moonracer]

There could be more than one fan. CPU, Video card, Power source. The CPU fan is easy, Video not likely unless it was expensive. Power source replacement is tedious. You hard drive may be going too. Does it sound like a jet engine?

[Fire_on_High]

Video not likely unless it was expensive.

HP has had issues with video card fans being bad for a few years now. I got a HP desktop as a gift last summer and am on my fourth or fifth video card already. Don't rule it out, but don't obsess on it either...CPU fan is still far more likely but be aware this flaw is out there and more common than the norm.