Thats a good budget GPU and should be able to go with a higher resolution so if you drivers are upto date then It could well be your monitor... try getting a resolution of at least 1920 x 1080
What monitor do you currently have and do you have drivers installed for it ?
I had the same problem the only way I've found to fix it is to go to display settings in arma and set the menu size to small the only other way is to get a bigger monitor
This issue is based towards your own personal setup, Get a wider monitor and it will be fixed however in the meantime as maxcolt advised go into the display settings and set the menu size to small