I have had ARMA 3 since the first release day on steam when it came out as Alpha, ever since I have had the same problem, even now in beta;
Game loads fine, everything is normal, once I get in game all I can do is walk around because if I shoot, get in a vehicle, open my inventory or anything for that matter, the game immediately freezes with no warning.
This has become really annoying as I have patiently tested this after every new patch came out, with no change to the result.
The other annoying thing is that the darn game will not close after it freezes, I cant end the game using any methods ive tried so far, forcing me to do a complete restart of my PC everytime!
Please help, im an avid ArmA fan, and I have never had any problems like these before.