I'm using an old HP desktop, no hdmi. On bootup display is too wide in both console and Gnome displays. Monitor controls cannot correct this so I experimented with the display control in Gnome. Somehow I turned off the vga signal. If I restart gdm3 the Gnome login window appears but after login the screen goes black and the no vga message appears. Rebooting the computer gives the same result. Any suggestions of how to decover?