you should check your nexon/combat arms folder for any hacks files (e.g .dll? ) if you do have any, you should probably remove them because HackShield has most definantley detected it and it is dis-allowing you to play. so yea delete any hacks files. and if you still want hacks, you just have to wait until next patch and next set of hacks come out.
1 thing you guys are forgetting. the firewall might be the problem. if thats the case, just put combat arms in the allow section. the firewall might be closing CA since it access's the internet and it thinks that CA might be a potential virus, thus it closes it xD