You must be dumping more heat into the PC enclosure.
How many Watts was the old graphics card and how many for the new?
Just for grins, monitor the CPU temperature. You might need to upgrade the case fan(s).
Alex
"There is a cult of ignorance in the United States, and there has always been. The strain of anti-intellectualism has been a constant thread winding its way through our political and cultural life, nurtured by the false notion that democracy means that "my ignorance is just as good as your knowledge."