During the campaign the game turns my pc power off like if it was overheating.
I know its not the case because I do play a lot more graphical and cpu intense games without this happening
Its odd because with skirmishes it does not do that at all.
That's pretty random. Make sure all your drivers are up to date, maybe also re-install GFWL? Also check your RAM.
Define graphical and cpu intense games since Dawn of war is one of the top ones.
It seems your haveing power problems where your gpu is not getting enough so it shuts down you pc.
Evil meet my Sword. Sword, meet Evil!