ok for months now i have had problems with arma not running on any of my systems ( 3 pc's and 3 laptops ) it just would not run .. so i started digging ..
for all of you here if you ever get this really strange problem ..
check your router and look to see if you have a setting on your f/w names Ping ( allow outside traffic to see you are there ) , that was the setting that was stopping it
allow it allways and you will have no problem running the game.