A few days ago, I turned off my laptop using the power button. Since then, my laptop hasn’t been connecting to my second display. I tried to connect the display through the display settings and using xrandr from Dom0, but it doesn’t detect the HDMI. It only detect the laptop main display. Can you help me, please? 
Did you update your dom0 during the last successful boot?
Maybe there is some issue with newer kernel, try to boot Qubes OS with older kernel version by selecting the corresponding boot option in GRUB boot menu → Advanced options for Qubes → Xen hypervisor → select kernel version.
3 Likes
Thank you very much for your help! You were right! I fixed it erasing the kernel last updating and the last installed packages from its latest version. 