Unable to enable Laptop monitor as Primary Mystery

Somehow the laptop display monitor on my EVO N610c has mysteriously been disabled. When the machine boots up I see a flash screen showing the Compaq logo but subsequently the only display signal is to the secondary monitor.
I am unable to set Primary monitor signal to laptop monitor at the Windows Control Monitor Settings tab.

The laptop configuration previously was working fine. The machine is on 24/7 and one day I came home to find that the signal just “disappeared” and I am clueless what event occurred to trigger this situation.

Any suggestions?