Something wrong with fans or is it something else?

I didn't know which section to post so I posted it here.

I have a HP Laptop ze4430us. While I am running it sometimes, I start here this really low buzzinf type noise and the computer starts to slow down incredibly. Now, I know the computer has overheated before and my first choice then is to replace the fan (I have been researching this for awhile). The only thing is that this can happen while the computer is cool and when the fan isn't running or even at times while it is running. On startup, while my desktop is loading, I checked out the CPU usage and it is way high and the light that shows that it is thinking is constantly on, now breaks. Finally after the comps loads(much longer then it is suppose to be) The computer runs very slow and continues the noise. The noise fluxaites up and down when the computer is performing tasks. One more thing, I thought it could have been my harddrive, but I ran the diagnostic for it and there were no bad sectors.

Are there two fans maybe and one is bad?

Its your hard drive.. theres nothing wrong with it. after they get a little wear on then they get a little noisy. Its probably got slow because you have more things on it. the light the blinks is what tells you when the hard drive is running or when the cd player runs.