This is fairly typical of an older (8 year old) PC tower that sits on the floor in a home or carpeted office. The dust gets on the fans, ruins the bearings, causing the fans to slow down and the parts to overheat. This one was too far gone and is headed for the boneyard...
Take the cover off and vacuum or (I prefer) use a compressor and a fingertip blower to blow the dust and grime out of the tower, power supply and various nooks and crannies. Keep the PC cool and it may last longer...
