It sounds like a faulty motherboard.
When you tried the other monitors, did you use the same cable - or did you try different ones? A faulty cable is often the culprit in cases like this. Have you tried using your monitor on another computer?
Samsung Galaxy S8 review
1995-2015: How technology has changed the world in 20 years
This 2D animation about monsters is illustrated in a Van Gogh painterly style
How to get WWDC 2017 tickets
Synology invites you to visit them at Insomnia on 26th – 29th August. Book your tickets now and visit Synology.