this happens with me on dawn of war 2. I still don't know how to fix it and I bought the game 4 months ago!
sorry, but I can't think of anything apart from the stuff you tried, which I also tried for dawn of war 2. If your desperate, you could always try reinstalling the game, or you could post your problem onto an expert website like expert exchange(you have to be a member) or something. Good luck, hope this helped.