When I boot up my monitor showed the in use light, then after a brief moment my monitor popped a box saying "No Signal" and went to standby mode. When I turned it off and back on I saw the usual screens and Windows booted up. The next two times I had to turn the monitor back on and off twice.
Then it got as far as showing the motherboard's splash screen before the monitor went to standby, but when I turned it back on all looked right.
Then it got that far again but after turning the monitor back on a second time I saw the motherboard's splash screen a second time. At first I figured it was a monitor problem, and that seemed to make sense as my monitor is ancient and the computer just a few years old.
But seeing that motherboard splash screen twice on a single boot-up made me wonder if the system was making more than one effort to boot Windows, as if the BIOS wasn't working properly, suggesting that maybe the problem was with the bios, and my motherboard was sick and dying.
Since then I just haven't turned the computer off.
I'm going to try a new monitor, since the current one is so old anyway, but I won't be surprised if the new one doesn't fix the problem.
I'd appreciate some opinions from someone who really know this stuff, which I don't.