It's most likely the graphic card as mentioned earlier.
If changing to another rendering mode in the ogre.cfg doesn't help, you'd probably need to install drivers for it in order to run the game at all.
If it was something with just the game the computer wouldn't restart. Maybe you run the game in a rendering mode the graphics card doesn't really work well with, the computer lose contact with the drivers and then force itself to a restart. Just because it wasn't able to recover from the last operation.