Check whether that heat sink is in contact with the processor properly. If this problem keeps on recurring, carefully remove the heat sink, reapply the thermal paste and put the heat sink back again.
Mine is an Athlon64 X2 4400+ and temp. has never gone above 51 degree C and that too in the afternoon in 40 degree C outside.]
For thermal paste, you can refer to this URL:
*www.amd.com/us-en/assets/content_type/white_papers_and_tech_docs/26951.pdf
Shin Estu G 749 is officially approved AMD thermal paste. Unless you can afford to lose void your warranty do not use Artic silver.