I have the same symptoms as Kleer - long initial loading time, then a bugged main menu. I'm on Vista 64, 8 GB RAM, GeForce GTX 260. I'm using the most recent drivers, and ArmA is patched to 1.16 with the beta patch.
The funny thing is that everything was working fine until a few days ago. The only change to my computer since then was installing Flight Simulator X, which really shouldn't break ArmA. I suspected corrupted files and un-installed ArmA (and deleted my profile), but re-installing didn't help.
Any ideas?
Edit:
Installing an older NVidia driver, 181.22 in my case, has fixed the problem.