boot – The second monitor turns black after grub

I am facing a problem in the boot process related to an external monitor.
I have a dual boot installation and, after choosing ubuntu on grub, the built-in and external monitor screens turn off if the HDMI cable is connected to the laptop. If I wait about 30 seconds and press Ctrl + Alt + Delete, I can start normally. I can not access ttys when the screens turn black.

I'm using ubuntu 18.04 on a 700 ideapad from lenovo with gnome 3.28.2. The version of my kernel is 4.15.0-42-generic. I'm using the nouveau drivers.