I assume you refer to the Intel(R) Core(TM) 2 Duo Desktop Processor E7400; if so, I confirm 85ºC is overheating, indeed. Thus, to begin troubleshooting, I'd recommend the tips found here:
I am sorry that you can't enjoy the happy computing. As per knowledge I can suggest you please purchase heat sink compound from the electronic market. Dismount the Processor from the Mother Board socket. Keep the processor upon a non electrostatic substance like as thick plastic board or rubber mat. Wipe out the old dried heat sink compound from the metal side of the processor with a cotton with Isopropyl (Not by thinner or Sprit). Be careful about the spillage of the isopropyl at the Pin side of the processor. Wipe the same with tissue paper properly. You have to clean the Heat Sink also. Now mount the processor in the socket properly & lock the socket. Now you apply the new Heat sink compound in processor & Heat sink in both and lock the Heat Sink with the mother Board by proper method. I hope this will work very fine, because, Heatsink compound helps to transmit the heat from the Processor to Heat Sink/Fan Properly. If the Heat of the processor can't properly transmit then the Processor may be over heated and cause disturb as you described.
Enjoy happy computing