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Does it work if you plug something else into it?
Maybe take it back / ring the shop for advice / new one, or if bought online, probably ring them for advice.
Just found this, hope it's helpful...
https://community.acer.com/en/discussion/495297/display-port-issues-with-the-predator-x34 - Video card conflicts
But, more importantly, the last entry discusses a VESA certified DP 1.2 cable (NO PIN 20) fixing the problem
Good luck :-))