you need to give more detail
to what step of starting combat arms do you get to before failure,any error messages,i have had popup blockers stop splash screen from coming up.but you need to give more detail,are you dowloading the current combat arms version?or reinstalling older one,firewall could be blocking,just completely turn firewall off,antivirus off,popup blocker off,redownload current version,delete old nexon folder after uninstall