symptoms:

 - idea splash screen shown

 - no project selector shown

 - when alt+ f4, "the do you really want to close?" popup shows (of course it does not show up when that popup is turned off in settings)

 - you disconnected a second screen recently

when working with double screen idea, sometimes when the second screen is removed, Idea seems to stay on the second screen. Try attaching a second screen and dragging it back down. You could also edit the second screen properties in settings to try to get it back.