TS2LC: Stuck on fullscreen, can't get borderless windowed

Alt-Enter is not working for me. When I use it, I get the Windows error sound chime. The game is stuck on fullscreen mode. I can't cycle to either windowed or borderless windowed. I'm a steam player.

I can't minimize the game. Pressing the windows key brings up the toolbar, and I apparently open other apps, but I never see the app windows or see my desktop. The Sims 2 stays fullscreen and running.