Monitor power cord connection.
This is just a little embarrassing. A couple of months ago I wrote about how it was taking my computer several seconds to wake up instead of waking up instantly as it has been for the last umpteen years. Last week Marc tells me a story about a loose electrical connection in an airplane.
Yesterday my computer was even more sluggish about waking up, and this morning I thought the display had gone to monitor heaven. Then I remembered that the power cable had gotten disconnected from the upstairs monitor for no apparent reason. I reach around back and push the power cable into it's socket and presto! The lights come on!
Thing about these flat panel monitors is that the power plugs are now vertical, so the cable is hanging from the socket. The individual sockets in the plug should grip the pins in the socket, but evidently it is not enough to keep them from working their way loose. When I pushed up on the plug on monitor a minute ago it didn't move, or if it did, it didn't move much, but it was enough to restore contact.