So a while ago I purchased an Acer H276HL monitor to replace an old Asus monitor that had developed some weird behaviour where it would get stuck in a strange mode, then just decided not to turn on again. This morning when I got home from the cafe I discovered that new monitor in a very similar state. It would respond to mode change requests, had the backlight on, and generally seemed responsive, but the screen was entirely blank/black.

I tried dozens of approaches, multiple operating systems, using Intel chips instead of AMD, using each and all of HDMI, DVI and VGA, suspending/resuming laptops while connected, ridiculous numbers of mode/resolution changes, lots of low-level commands to suspend/resume/poweron/poweroff, Acer's (non-functional) configuration utility, and anything else I could think of to get the monitor to pop out of that weird state.

In the end what worked was, in KDE, setting the mode to 720p, rebooting with that setting intact, and then, when the monitor came back up with crazy corruption (but something showing at last), re-re-seating the DVI cable and then switching to the native resolution.