Apparently alt + enter works now, try that before continuing.

Some people seem to not know how to check. So just to make things simple, here is a website that can tell you. Open it on the monitor you want to use if you have more than one. Refresh to update it if you moved it to another monitor.

http://www.whatismyscreenresolution.com/

There are also multiple ways to check through your OS.

You'll want to start off by finding your Cortex Command folder. For most of you, it'll be in C:\Program Files (x86)\Steam\SteamApps\common\Cortex Command once you are there, go to the base.rte folder and open Settings.ini.

Another way to find the files would be to go to your game library, right click on Cortex Command and press properties. Go to the Local Files tab and press Browse Local Files. After that, go to the base.rte folder and open Settings.ini.

First, I recommend saving the file somewhere else, just in case.

Now that you are in the file, you will need to know your screen resolution. This can be found by right clicking your desktop, and pressing screen resolution. Mine for example is 1366x768.

Resolution is formatted as such: (X) x (Y)

Now change the following:

1. ResolutionX = Your resolution's width (X). So if you have a 1366x768 monitor, it'd be 1366.

2. ResolutionY = Your resolution's height (Y). So this would be 768 if you had 1366x768.

3. Fullscreen = 1

4. NxWindowed = 0

5. NxFullscreen = 1

After you have done this, save the file and exit, if it doesn't let you save because it is in Program Files, then save it to your desktop and drag it into the folder and overwrite.

Now you should be good to go, just launch the game and see if it works.