Samsung monitor no longer goes to high resolution
I have an iMac, about 2015, running Sierra 10.12.6. I have a Samsung 32inch external monitor (2560x1440).
All of a sudden, when I started my computer up this morning, the Samsung does not go to high resolution.
Out of the blue. It's worked perfectly for 2 years. Like it got amnesia.
I go to the usual display set up, and use "Default for display" and the monitor and computer think that the default display is the lesser one.
Help? Thanks.