This reminds me of my infamous GTX 480 back in 2010. Temp while idle is 48*c and full load is 85-91*c. After cleaning the fans of dust and dirt, temps were a little okay 43*c in idle and 85*c at full load. But alas after 7 months of heat torture, it died peacefully in November 2010. Didn't have/know any thermal paste back then... I agree with Sir Goldfries, opening the side panel won't do much. Better change to aftermarket cooler or liquid cooling if budget permits.

Could also be related to the bios? Maybe trying to update it? But chances are, your symptom is more towards problematic cooling. Better prepare for a new GC.