It looks like you may be on Windows 10. Sometimes the monitor settings can get stuck where it thinks another screen is active (even if its not). On Windows 10 you can press the Windows Key then P and choose PC Screen Only to try to get it to show on the Laptop Monitor.

No, that's not it. When it starts-up I see in the bottom left something flashing, and then it's dead. No screen. I reinstalled the software but that did not help. So, something in the registry perhaps is broken??

Thank you! You're a life saver. After changing the resolution I was able to open the screen and it loaded up the client list. Was not able to click anywhere, as the Lacerte application did not respond, it did not receive the clicks. Then I restarted Lacerte and now it came back on the screen and behaved normally. Thank you!

an option that has worked for me is holding alt and space bar.

Nope!  The problem is the inability to type anything into the Password field on the 2019 sign in screen.