Sounds like heat/ cooling issues. Try cleaning your fans, ensure they are running. They might not be running fast enough for cooling properly, may need to replace. That is a high temp at idle for sure, mine runs 45C at full load (AMD 4000+, 4g ddr 333, 7900 GTX) but I also use 2 80 mm fans, and a 120 mm side fan + the chip fan.
Good Luck,
Oz