My computer is overheating when I play games. What is happening?

Check the inside of your case for dust buildup. This could solve the problem right away. Many of us do not dust the insides of our computers, but you would be surprised how much dust gets inside the case.

Also, your heatsink (the aluminum thing on top of your processor with a fan on top of it) could have a bad connection (thermal paste could be applied incorrectly). Thermal paste helps with the transfer of heat from the processor to the heatsink. The heatsink dissipates the heat to cool your processor.