Did you download from the source listed on the official (this) site? I have seen this problem before on Windows Vista AND 7. The problem was one of two things in all instances: 1.) Windows asks if you want to allow the program to access the internet after the first time you try to start AC. If you don't click allow, then it will close everytime thereafter you try to open it, in most instances 2) AC was downloaded from some 3rd party site instead of from official sources, and the included .bat file was corrupt or altered in some way.
Try this: a)Uninstall AC. b)Update windows. c)Reboot d)Download AC again from the official sources (http://assault.cubers.net/download.html) e)Start AC f)Make sure you click "allow" if asked if you want to allow the program to access the internet.
Try this: a)Uninstall AC. b)Update windows. c)Reboot d)Download AC again from the official sources (http://assault.cubers.net/download.html) e)Start AC f)Make sure you click "allow" if asked if you want to allow the program to access the internet.