Find your video card in the device manager and uninstall the driver.
Reboot, windows will reload the driver.
Test.
Is there a driver disc that came with that monitor?
I have a AOC Q2770PQU monitor which has a resolution (native) of 2560 x 1440.
On my pc Win 10 now has a max resolution of 1920 x 1080. It also has my monitor as a AOC 2770G4.
Help would be appreciated in sorting this out.
I have dual monitors, my other secondary monitor is a LG and it is behaving normally.
I think this problem arose after a crash, in that I came back to my bit PC expecting it to be on, found it off restarted and found this problem.

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