I have seen this problem before when my old AMD FX processor and 7900gt started to kick the bucket. What I did was get a new cooling fan for my 7900gt, then I took the case side wall off. This worked, but chances are the capacitors are going bad in the GC. Don't bother with all the new fans unless you don't have any in the case right now. Just open the side and if you are really worried about it get a desk fan and point it into the open side of the case. That will work allot better than putting a bunch of new fans in a closed case.