The monitors don't have software menus. They just have a couple of knobs for adjusting contrast/brightness and a couple of buttons for adjusting screen size/position. I tried power cycling but no ...

If you see the Power Button Lockout message on your HP Monitor, press and hold the power button for about 10 seconds to restore its functionality.

I kept pressing the wrong buttons on my display when changing the input or messing with the settings. Then the dim lightbulb in my head flickered to life.