Sorry to hear that. Maybe the window lost focus (in which case clicking on the window should solve it), or maybe it is related to the way input was assigned. Currently, only directional arrows work (in the upcoming update there will be WASD and joypad), and I did not have the time to set a proper input map, these are the basic Godot ui_up etc. so if there were a compatibility issue, I guess it can break the game.
Regardless, thank you for reporting your issue :)