Clean out your computer. Dust buildup is a very common cause of overheating
Go to an electronics store, or just a store with a decent sized electronics section, like Target or Walmart, and buy a can of compressed air (looks something like
this)
Take off the cover of your PC, and spray out any dust, especially on and around fans and exhaust/intake ports
Make sure you hold the can rightside up, or it'll spray freezing liquid instead of air