The sims 3 shuts off my computer. What do I do to fix it?

It happens every time I play the sims 3 for more that an hour. I'm playing the game then next thing you know my screen goes black and my computer shuts off. It's starting to p**s me off because I end up losing my essays from accidentally forgetting to save them. I'm running windows 7 64x bit, AMD Athlon M320 (2.1 GHz), Ati Mobility Radeon HD 5470. I have Sims 3 base game, world adventures, high end loft stuff, ambitions and generations installed. And before you ask about mods it was happening before I even realized there were mods. I used the ultimate fix to get the game running and I followed it to a tee. I tried un-installing and reinstalling and I still get the same problem. What I realized also is that if I try clicking to get out of the opening movie it doesn't respond right away, which I found is a sign at some point the game will crash.

It might be an issue with your computer temperature. Either install GPUTemp or start cleaning your GPU for dust. See, if a computer is too hot, it shuts down. It does this to prevent computer-exploding. You really should save your essays, erm, maybe finish them before playing. Hope this helps!