Arctic Silver 5, aka AS5, is crap, I bet toe-jam would work as good. 80C is way to high for a AMD cpu. You need to shut it down, remove the heatsink, clean the old paste off the heatsink and the cpu, and re-apply a little new paste (whatever brand you have). Did you remove the fan from the heatsink? Make sure the air is blowing into the heatsink. I agree with carnageX, get some Tuniq TX-2.
Newegg.com - Tuniq TX-2 Cooling Thermal Compound
Newegg.com - Tuniq TX-2 Cooling Thermal Compound