DIAGNOSIS This is the device getting stuck in a software or sleep state. It's not fully off, but the screen and audio have crashed while the core Alexa process is still running.
FIX Hold down the microphone off and volume down buttons at the same time for about 15 seconds. You'll see the screen flash and it'll reboot. That's a full system restart and should bring everything back.
IF THAT DIDN'T WORK If the light ring isn't even on, the power adapter might be the issue. Try a different USB-C cable and a different power brick. The Echo Show 5 needs a decent amount of power, so use the original adapter or a good-quality one.
HEADS UP If this happens constantly, check for a pending software update in the Alexa app under Device Settings. A buggy update can sometimes cause this loop.