I am really sorry to hear that your laptop is acting up especially during gaming sessions that we all love so much
. Specifically due to aforementioned fact (it occurs while playing games) it is certainly caused by overheating. I was going to mention how you could possibly fix this, but somebody else discussed similar issue on the following link:
Aside from the tips that are mentioned on the other thread, I would recommend to check for updated graphic driver (assuming that you have Nvidia Optimus graphics config running under Windows 7 32-bit) from HERE
I have a similar model (N82JV) with upgraded CPU and Nvidia 335m as opposed to yours 325m, but essentially build around very same chases. I had played plenty of games on hi-res with zero overheating problems. If you'd like you could also download MSI Afterburner
graphics tool which I can attest works perfectly with Optimus graphic config that we both have in our machines, and allows you to view/log lots of stats pertaining to your graphic subsystem. I'd suggest to log the temperature data and see whether there are some extreme values after one of the "play game, laptop turns off" events. First of all though, follow the thread link above and see if some of the tips won't help better.
Good Luck...Hope that you'll work it out