i got the problem solved:
i tried an other gfx card -> it worked.
i inserted my gfx card again -> it still works!!!!
guess the gfx card wasnt inserted correctly or some loose connection.
nevertheless: it´s working!!! arma3 i am back.
hope for you guys you will get it solved, maybe try an other gfx card or put your out and put it in again :/
sry 4 my bad english :P