When was the last time, you cleaned the computer inside?
If you haven't done this for about 4-6 months, then do it now. If you decide to clean the dust off your case, make sure that you don't touch any circuit boards or components without grounding yourself. An easy way to do this, is to keep one hand on the computer's metal case, while using the other hand to clean.
As for the CPU temp reading...
Try going into your BIOS settings, and go through all the menus to see if there is a temperature reading.