This happens to me every time. I usually just wait about 10-20 seconds and everything is normal.

We need dxdiag and files from this folder for solve your problem. C:\Users\<Name>\AppData\Local\Arma 3 Alpha\
Can you upload somewhere in winrar package please?
When package will be smaller than 2,097k, so you can attach here. Thank you.

http://feedback.arma3.com/how-to-user.html.html

Closing due to lack of info / response.

If the issue is still reproducable for you, please create a ticket for it.