Solved: World of Tanks FullScreen not working
Full-Screen Mode Solution Poll
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Solution to Full-Screen Mode not working in game
For my system the solution was quite simple. I had TeamViewer running in my system tray which includes some integrated options for windows. When I closed TeamViewer and attempted to set Full-Screen Mode in World of Tanks, it finally worked.
This may not be the reason your's is failing to work. However, the same principle applies to a lot of applications. If any third-party tool you have loaded attempts to capture the display, such as logmein, or possibly third-party software used for recording Game Sessions and attempt hook the Game Window they could interfere with your game's ability to go full-screen.
Good luck and feel free to comment with other applications you have discovered that keep World of Tanks from going to Full-Screen Mode.
Screenshot of WOT in Windowed Mode
No matter how you launch World of Tanks, it will not allow you to set it to Full-Screen. Windowed Mode, and Windowed Borderless Mode's work fine in all resolutions.
However, no matter how you attempt to tweak the game Full-Screen mode will not set.
Many people have reported they have reset the Game's Graphics to default. and that still did not resolve the issue.
One sympton of the issue is the game appears to minimize to the desktop, then after the "save screen settings dialogue timesout the game returns to the previous mode.