Have you tried booting Ubuntu with just one monitor attached? This may be worth a try to narrow down the source of the problem. See: https://wiki.ubuntu.com/X/MonitorDetection
Good luck.
Have you tried booting Ubuntu with just one monitor attached? This may be worth a try to narrow down the source of the problem. See: https:/ /wiki.ubuntu. com/X/MonitorDe tection
Good luck.