debonairy

It might be time to clean your computer because the dust built up inside may be having an adverse effect on the cooling system. I've had a laptop die on me because I put off cleaning it till the next week and the GPU got fried before I got around to it. The laptop was shutting down on its own due to overheating issues like your computer.

The best way to clean is to open up the computer and use a mixture of 50% water and 50% isopropyl alchohol. Use a clean lint-free cloth like those used for cleaning spectacles and try to use light dabs of the cleaning mixture and not make the cloth too wet. Usually the fans will be the dirtiest followed by the heatsink. Give some time for things to dry before replacing the computer case and switching it on.

Alternatively, you can use a can of compressed air to blow the dust away but this doesn't work so well for me. Hold the fan blades still by using a pencil or toothpick and try to blow such that the dust flies out instead of into the computer.

If you are using a laptop then placing a book under the side with the screen so that the bottom is angled off your desk will also help a little with cooling.

Hope this helps