Can't use 1920 by 1080.

[sloopsloop 0]

I have a problemo on Dayz and Arma 2 in general, the problemo is that I cannot change resolutions because when I change the resolution back to 1920 by 1080 it WILL not go back.

Why is this?

Also why can I not put the display size of my icons in the bottom corner (the drink food and blood icons) higher than extra small. If I put it any higher it goes of the screen.

Before anyone asks if my monitor can use the 1920 by 1080 it can.

Thanks in advance.