Screen flashing colors at start up

Hello, 

I really face problem with my laptop screen ( DELL XPS 15z). Its flashing colors at start up. I update all necessary software and made diagnostic test. Everything is OK. But still flashing colors.

I found that if I  plug in the charger, the screen will work normally. BUT if I did not plug in the charger, most of time the screen will start flashing colors at start-up and I can't do anything except restart  or fold the screen and charge my lap. 

Plz help me to fix it. find the attached.