Slow browsers load

My desktop comes up as usual. But all my browsers take along time to load. I've tried the msconfig thing. I've uninstalled and reinstalled my default browser. I've tried everything I have read in forums. All to no avail. My pc when first turned on makes a loud noise for about 20 sec's. I think it's my fan going out. At around the same time the fan quiets down my browsers load and continue to from then on until my pc is idle for a time and goes into hybrid sleep. When I wake it up all the above happens again. I have been checked by a knowledgeable friend that I have no malware or any infections at all. I read in a forum where someone had the same problem and the answer was that it was the pc itself. Dust build up, in my case cat dander, and most of all the answer talked about the fan going out. Does anyone think that might be the problem? My knowledgeable friend is coming over tomorrow to see about me buying a new fan. I do not have alot of money. I can wait a little longer to replace the fan in then future. What is your opinion. I have win. 7/32 bit/ year and one half old custom pc. Avast Internet Security, Mbam pro.