What is your operating system?
You will have to either edit your configuration file by hand to disable fullscreen or launch the game in windowed mode.
In *NIX operating systems, the easiest way to go would be to launch the game by passing it the "+vid_fullscreen 0" argument from a terminal:
Code:
cd /path/where/the/xonotic/binary/is/
followed by
Code:
./xonotic-linux-sdl.sh +vid_fullscreen 0
or, in Mac OS X,
Code:
open Xonotic.app --args +vid_fullscreen 0
In Windows, you can do the same thing in the command prompt using the following:
Code:
xonotic-sdl.exe +vid_fullscreen 0
after getting into the right directory using the cd command.
You could also follow the instructions in
this post but replacing -nosound and -nohome with +vid_fullscreen 0
You can also locate your config.cfg file and edit it with a text editor to change the vid_fullscreen line from 1 to 0 or change the vid_width and vid_height to the right resolution. But [b]please[b] don't use Notepad or Word in Windows to do that: I can't guarantee it will get the line endings right and you might screw up your config.cfg. The problem with that is that config.cfg's location (the personal data directory) depends on your OS and I can't tell for sure where that is. In Linux, it's in ~/.xonotic/data. In Windows, it's sometimes found in your User directory under "My Saved Games" or somesuch. That's all I know.