it really is confusing but the ArmA games sometimes when you buy them, never work apparently.
try contacting Bi-Studio (the devs for the ArmA games)
And try going here to see if you can run the game-
http://systemrequirementslab.com/cyrijust select ArmA II from the list.
it will ask to allow to install a plugin, click yes. no viruses are with it, trust me, i use it all the time.