Sorry,i've just sold the problem.

here is my arma3 folder:
[link]https://rapidshare.com/files/1433065052/Arma%203%20Alpha.rar[link]
but i don't understand how do i get the DXdiag
sometime the game lag a lot(one frame for 10 or 20 seconds),but if i wait it can back to normal,it realy crash only one time for five "big lag"...and i can ear the other player speaking during the lag time...

hello i got the same problem,and it happen also since the latest stable built have been installed