So I had this problem with my workstation that the screen stopped
diplaying abything, and the monitor simply diplayed "no signal".
After loggin gin via ssh into that workstation kernel messages
showed that the amdgpu driver also detectd a loss of connetion to
the screen via the DiaplyPort and gave up after three tries.
  Even after a reboot, cold start and hard power off the monitor
didn't turn on again, "no signal". Ugh. No good.
  Fiddled around with the monitor. No go
  Plugged in a laptop to the DP-cable leading to the screen: Work!
  OK, so it can't be the cable or the monitor, right?
  Damn, it's the graphic card. OK, anyway, I got this graphic card
used with the workstation (used) and I think it's manufacturing date
was somewhen in 2016, so well beyond retiremend age. God speed, old
mate!
  Went and bought a new graphic card. Power on... success! But then,
after just 10 minutes... "no signal". This felt like an episode
from Scooby Doo, "So it was the monitor after all!"
  I was desperate and already contemplatinmg buying a new monitor -
I also felt really stupid, as this kind of shows that the old
graphic card probably isn't broken after all...
  As one last ditch-effort I tried to connect the cable toother
ports on both the graphic card (it has two DP) and the monitor.
1-1... no. 1-2... no. 2-1... no. 2-2... no. OK, let me find an HDMI
cable because bot the monitor and the graphic card have one. While I
was searching for the HDMI port on the monitor I found *a frigging
third DisplayPort*. 2-3: SUCCESS!
  And it's working ever since... 
  I guess that I need to to retire this monitor at some point as
well, but for now it seems to be working. Ugh.