I believe this is caused by an incorrect registry entry, which is VERY rare.
You can try forcing the game to launch in the correct resolution by setting some additional parameters in a shortcut.
1. Right click the game exe and create a new shortcut
2. Right click the shortcut and select "properties"
3. At the end of the "Target" textbox, add the following, leaving a space after the quotes: -screen-fullscreen 0 -screen-width 1280 -screen-height 720
This is how it looks on my PC (it's in Spanish but it should help you identify where to add the parameters)
4. Save the shortcut
5. Launch the game using this shortcut.
Once you've launched the game, you should be able to set your desired screen resolution in the settings menu. Once you've done that and closed the game, you should not need the shortcut anymore and just double click on the exe to launch the game.
I hope it helps.