Ok so first we need to get to the file that will let us change it to be able to actually see the game.
So, First: go to the Local Disk or (C:) Drive
Then, find Program Files(x86)
Now open that and scroll down until you find a folder named "steam"
Open that folder and there should be another folder called "steamapps"
Click on that and then click on the folder called "common".
Here you should notice that there are folders with the same names as all the games you have installed from steam. This is where all the internal files of all your games should be.
Now click on the Unreal Tournament folder and then click on "system"
Now scroll down until you find Unreal Tournament.exe and under it should be UnrealTournament.ini, open the .ini file.
Open that with notepad or wordpad, it doesnt matter and scroll down until you find this:

[WinDrv.WindowsClient]
WindowedViewportX=1280
WindowedViewportY=768
WindowedColorBits=32
FullscreenViewportX=1280
FullscreenViewportY=768
FullscreenColorBits=32

The numbers wont be the same as these but the words will be, you need to change the numbers to these and it should run the next time. If not check your screen resolution and plug them into where the viewports would be.

There you go for anyone that cant play the game, i hope this helped. :)