Hmm that's weird :/ tried updating graphic drivers? And how much RAM do you have? Could be a memory issue. Not sure but could be.

Open your steam folder and then into steamapps, then common. Open the ARMA 3 folder, right click on arma3.exe and go to compatibility tab and select run as admin. Apply and then right click on arma3launcher and in compatibillity tab, set it to run as admin and click apply. It fixed it for me. Btw try to use google since this has been answered many times. Takes 2 minnutes. You have many people trying to help here but you can also help yourself ;) Hope the admin helps.