Also had a GTS 250 prior.
Thing is a power hog and gets hot.
Could easily be a PSU problem.
Although, I had a Pentium D and my GTS 250 running on a stock 375w PSU. Both parts were energy hogs that loved to get hot. Never had any problems though...
What are the specs for your PSU? Or better yet, do you know the model?
MY PSU is a 'Gigabyte GE-P585A-C2' Peak Wattage is 585W