I am having the same issue as Buzzcut13. When i load up anything to do single player i have no control over any units the only thing that happens is a still camera view of scenery that i cant control. I have uninstalled and reinstalled with these issue still persisting. I have played over 70 hours of Arma2 OA and only now has it decided to do this.
Windows 7 64bit
Intel Core i5 2500k @3.3GHz
8GB RAM
Radeon HD 6970