The graphics cards are designed for gaming (well, they are if you got one for gaming!), so they can run a bit hotter than the rest. However, once you go over a maximum of, say, 80 degrees Celsius, then you are looking at a problem.
That's just on the graphics. The rest of your CPU shouldn't be getting any higher than 50.
Time to give it a bit of a dust, see if that brings the core temperature down?
http://wizzley.com/pc-dust/