For check in what mode your game run (sometimes she can run on window mode by default) go to "Documents - AlienShooter2 Reloaded Saves - Saves" and open "_global.dat" with some text redactor. Here you need "iFullScreen=1" https://prnt.sc/qFsWUlD8KQnx where 1 mean- fullscreen, 0- is a window mode. What if game run in a window mode? Ofcourse it's more comfortable to play especially you have 1 monitor. BUT, loading between levels will take much more time, and due to the fact that game did't have autosplitter that cannot be use for the runs.