not running dual monitor, or some other not so normal stuff?
Nope. When it is preparing the lightmaps on complex scenes, it may seem to do nothing for a while. Could that be it?
Nope. More precisely, while I understand it can be unresonsive (though I think it's a pretty bad thing that it hogs the entire computer for more than 30 seconds - and when I say completly it's completly), the problem is why does it change my graphics mode? (and also why did it block again - apparently forever - when I try to kill it?)