Thank you for the tips on the heat sinks clogging up with dust.
My Dad is a retired IBM engineer and to my surprise knows nothing about computers! I bought him one from work, Dell Optiplex GX 280, the lease had run out and the employees had first dibbs. I set it up and had him buy Symantec AntiVirus. His cable modem is with roadrunner and roadrunner offers this "free" internet security package through CA security. Of course it's only free for the first year, anyways, I said ok we'll load it and see what's what. I only loaded the spam blocker and antivirus apps. Well a couple of weeks ago he called and said his computer kept telling him he needed an antivirus program (a pop ups). he was getting these bogus pop ups on the desktop because he downloaded a bunch of crap! Now I don't know if he actually has a virus yet, but he has really messed up his machine. I was not a happy camper. Anyway, he now has all this spam loaded and possibly a virus that the CA Security suite is not picking up. It's all quit embedded in registry. I have found some sites that have some possible fixes for the thing. We will be loading the Symantec product once I get it half way running decent. I see know that him having a computer might not be the best thing 
Concerning viruses or getting rid of most or all of it, first find the McAfee stinger at their site and follow the instructions on the site. Site:
http://vil.nai.com/vil/stinger/. Then download Avast Home Edition virus protection Site:
http://www.avast.com/eng/avast_4_home.html. You will need to register, but it's free and works very well. Or your can use this product, AVG, which is equally good and free also. The link is here:
http://free.grisoft.com/doc/5390/us/frt/0.
Both of these do virus data updates almost daily or as new viruses are discovered. These are the ones that us PC propeller heads use for home. Norton is a waste, has it's own problems and appears to miss a few, at least in my opinion. And McAfee is very good, but is always asking for a reboot and both of these cost ya monies, which I'd rather spend on chrome.
This should get ya back on the road of cleaning and keeping the PC/laptop safe. It's a start anyway. There is more, but is a bit more work. . .If you do not use virus protection and can just about guarantee ya that in about 5 minutes on the internet, you'll get hosed with viruses etc.... Once your all clean and running good, especially if it's a relative, get an image off the the PC/Laptop and keep it for future use. A good habit to get into. Also, keep your data in
one folder and back it up every week or more! Ok, I'm gone...I've talked enough. Hope this helps.
Ugly John