Computer stops responding when playing Amnesia

[Mooserider]

So, I posted a while ago here about this, and Plutomaniac (Sorry if I spelled your name wrong) kindly answered, and I tried giving it a go but nothing's worked and that thread disappeared. Anyway... on to the actual problem. Whenever I launch amnesia it will run fine for about 5 to 10 minutes. Then, my computer will just die. All my lights stay on, like the computer's still running, but the monitor goes black as if I turned it off and says 'No signal'. I've tried moving the mouse, turning the monitor off then on again, even unplugging it then plugging it back in, but the only way to get it working again is to do a hard reset, by holding the power button in until it turns off then turning it back on again.

What I've done:

- Updated the graphics drivers. I've got the latest Nvidia drivers.
- Running the game on lowest settings. I've got it windowed, on the very lowest settings but the problem still occurs.
- Using keyboard short-cuts to check if the computer still responds. I pressed Alt+F4 and enter (Usually shuts the computer down) but nothing happens.
- Checked for overheating. I felt how hot my computer was just as it had crashed, and it was quite cool.
- Defragged and verified (I'm on Steam). No success.
- Other stuff I think, but I can't remember.

Also:
- I have Windows Vista.
- I usually play in windowed mode (I don't know if that would matter)
- I've had Amnesia since September last year. I believe it started happening since I started using the developer tools, so therefore if I can't get any other answers I'll get rid of them.

I wanted to see if any other people have had similar problems with the tools, or if anyone has a different answer, before I remove the tools though.

Thanks in advance.