Guide link

Make sure your game is Version 1.4 you can download a patch from this link:
https://web.archive.org/web/20071218061808/http://www.giantswd.org/download.php?offsite=0&id=931&d=patches/patch-1.4.exe

then install the beta patch 1497:
Download that from here:
https://www.giantswd.org/index.php?file=60
(download link at the bottom of the page)

and install it, and during installation make sure the install directory points towards your steam version of the game!! the installer has a tendency of adding \Giants - Citizen kabuto\ to the end of your installation path, make sure its just the normal folder!!!!

Folder should look something like this:
C:\Program Files (x86)\Steam\steamapps\common\Giants Citizen Kabuto\

and now your game should be working fine and fullscreen 1080p.
this should also fix multiplayer.

some people also have issues with mouse movement,
you can fix that by adding a launch command called "-framelimit [number]"
Right click the game and go to properties and click Local files
now right click the .exe for the game and click create shortcut and drag it to your desktop
right click the shortcut and go to properties and go to the shortcut tab
in the target box go the the end of the line behind the " and add "-framelimit [number]"
then change [number] in 30 or 60 whichever you prefer for your frames and apply and ok.
now everytime you want to play the game you launch through this shortcut.

to show your appreciation for this guide, just hit a thumbs up and leave a nice comment :)

if you want to then share and favorite this guide too, ill appreciate that :D

have fun playing guys!!!!