I'm having the same problem. Just downloaded complete 1-4 build. When I try to run, it switches momentarily to a black screen then back to desktop. The first time, I saw a message from Microsoft Security Essentials but too quick to read. I disabled 'Real Time Protection' in MSE in case it was that, but no difference. I reduced game speed and detail to minimum in setup but still no difference. Win 7 32 bit with 4G RAM. I'm itching to play, so all suggestions gratefully received!