IN MY OPINION, you're facing a thermal shutdown. You can play at that displaying settings for 5 min until the system shuts down.
1) Use throttlestop and run it in PERFORMANCE MODE. Play the game for 15/30min (if you can) with that program opened in that mode/profile.
2) Use throttlestop and run it in BATTERY MODE. Play the game, or let it play by itself for 1hour with that program opened in that mode/profile. I know the game will not run but instead, walk, lol.
If it is a thermal shutdown, in Performance Mode your pc will shutdow, but in Battery Mode, your pc won't shutdow BUT your game will be unplayable. (obviously)
If all these conditions are met, you should repaste your CPU and GPU and remove all the dust inside your case in the process of opening it.
The 1st gen. intel i7 BECOME EXTREMELY HOT, and the ATI cards are also known to reach high temperatures.
You tell us you were using Solidworks when the pc turned off. If you were normally working (designing, changing colors, creating objects) i bet in a GPU high temp, if you were Rendering i bet in CPU high temp.
Once again, this is just one hypothesis but IMO if the game stalls every 5 min and the pc shutsdown for no apparent reason this is a thermal issue.
PS. intel i7 920qm: It can perfectly reach 90 to 95 degrees and the processor will still be OK. The cooling fan is in charge to keep that temperature there.
If the processor temperature reaches 100°C or more it will send a signal to the motherboard to shut down to prevent mayor damages and most likely it won't be possible to turn the computer back in until it cools down.
