So recently, well not recently, my computer has been restarting randomly. Normally it's while my sister and I are playing Sims 3, but sometimes it'll just do it on its own. I have a feeling it's because the computer is over heating. I believe this because the back top part of the computer is normally very hot after it resets. And also, the room our comp is in can get up to 79 degrees.
I always have the fans running at max, but is there anyway I can fix this so that it doesn't happen all the time? It can get very VERY annoying.

Any help would be great.

Almost all overheating PC problems are cause by dust.

Get the case open and use compressed air to blow all the dust out of your machine, off the fans and heatsinks especially.

9 times out of 10, this is all you need to do