I have this weird problem with my dual monitor setup.

If I connect my hdmi cable to my secondary monitor, everything works fine, and I can see both my laptop screen desktop extended to the second monitor, but If I reboot my system, or startup with the screen connected, I only get to see the extended desktop on my monitor, while my laptop screen is 90% darkened- not totally, I can still shut down my system if I strain my eyes..

Any help please?

thank you