My laptop fan is always running , why?

i have scanned it for spyware and viruses and nothing. my cpu seems to be running low. there is a driver that i can't seem to fix but i'm told i don't need and i can't get rid of it. so now i have looked at others with the same question and all the answers are duster duster duster!! that can't be all there is to it? my fan runs all the time while i use it and when i put the computer to sleep. i ran out of duster a while back so i will get some and try it but maybe someone knows about something else that could be making it do that.