sounds like a bad case of mucky processor !!!!!
Open the box .... have a look at the processor heatsink/fan
if it looks like a dandelion clock .... (or something the cat coughed up) it needs a clean
you need a softish brush (I use one of the wife's blusher brushes) .... or a half inch paintbrush ... give it all a good going over (be careful - but get into all the nooks and crannies)
then if you have a vac with tools ... suck the dust out of the bottom of the case (don't get closer than 3-4" from the processor!)
while you are at it you can safely give the power unit a good going over.
that should solve your problem.