If you have changed your resolution in order to play Hell Let Loose and now you can't click on anything there is a simple solution that may help!
You can start by launching the game and pressing Alt+Enter to go into Windowed mode where you can then change the settings again.
If this doesn't work, you can reset your entire game settings by following these steps:
Click Start, type %localappdata% and Enter
Open the HLL folder and go to Saved > Config > WindowsNoEditor
Delete the GameUserSettings.ini file
Launch the game and retest after saving your settings!