I had a gears of war problem as well, it took me two months but i fixed it finally. It was crashing soon after it was loading, the problem was windows live. You have to uninstall your current version of windows live and download the new version from Microsoft's website. For some reason when you install games from Microsoft it doesn't update the version. I accidentally came across this when i couldn't get Universe at War to work either.
I installed the new version and it worked, tried gears of war and all of a sudden that was working also. So if you haven't already give it a try!