Comment 6 for bug 1762200

I found the fix/solution; i tryed delete unknown screen(CRT-0) from nvidia-settings but its shows "Failed to generate X config file!" and i checked /etc/x11, xorg.conf was missing
So, i copied my 17.10 xorg.conf to 18.04 now its working i can see gdm greeter

Also, this line caught my attention(xorg.conf line:30)
Option "IgnoreDisplayDevices" "CRT"

~$ nvidia-settings

(nvidia-settings:18214): dbind-WARNING **: 23:26:48.227: Couldn't register with accessibility bus: Did not receive a reply. Possible causes include: the remote application did not send a reply, the message bus security policy blocked the reply, the reply timeout expired, or the network connection was broken.

** (nvidia-settings:18214): WARNING **: 23:26:48.468: PRIME: Failed to execute child process “/usr/bin/prime-supported” (No such file or directory)
** Message: 23:26:48.468: PRIME: is it supported? no

WARNING: Unable to parse X.Org version string.

Package xorg-server was not found in the pkg-config search path.
Perhaps you should add the directory containing `xorg-server.pc'
to the PKG_CONFIG_PATH environment variable
No package 'xorg-server' found

ERROR: Unable to find a display device for screen 0!

ERROR: Failed to add X screen 0 to X config.

ERROR: Failed to add X screens to X config.