System:

Motherboard: ASRock B450M Pro4

CPU: AMD Ryzen 5 3400G

Graphics: GeForce GTX 970

Monitors:

  1 on GeForce GTX 970 via DisplayPort (2560 x 1440, 144 Hz)

  1 on Onboard via DVI (1920 x 1080, 60 Hz)

  1 on Onboard via VGA (1600 x 1200, 60 Hz) <- this one is the problem

Other info:

I'm dual-booting with Windows 10, where there are no issues with the third monitor. I've changed the BIOS to set the external graphics card as primary, but the BIOS and boot screen still display on the onboard VGA monitor when it is connected. If the onboard VGA is disconnected, they display on the onboard DVI.

Problem:

When the onboard VGA monitor is connected at boot time, I see Ubuntu start (there are a few errors which also occur if the VGA monitor is NOT connected), but no login screen appears - the monitor gets no output shortly after boot.

If the VGA monitor is NOT connected, I get the login screen on the onboard DVI monitor. I can connect the VGA monitor anytime after the login screen appears, and it works fine.

What I've Tried:

• Two different VGA cables and a VGA to DVI cable - no change.


• Copying monitors.xml to the gdm user (as per Is there to make the login screen appear on the external display in 18.04?) - this will cause the correct monitor to display the login screen when the onboard VGA is disconnected, but if the onboard VGA is plugged in, there's no output.


• Enabling and disabling Wayland - no effect.


• Pressing ALT + F2 after boot - no output.