Recently I am having the following problem:
Let's say I turned off the PC at night, by shutting down in OS and by turning off the electric switch at the plug.
When I wake up in the morning, I would turn it back on, and press the power button at the case.
Normally it would start and the monitor would display those BIOS thing and OS loading screen, and finally the desktop, with that OS entry sound.
Problem is now when I start the PC, the monitor would be in its "got power but got no display signal" mode, but I know it continues to start up because eventually I can hear the OS entry sound. The strange thing is if now I switch off and back on the power to the PSU and press the power button at the case again(sometimes it's auto and I don't have to press the button and I don't know why), then there would be chance that the monitor display normally without problem, until I shut it down at night and having the same problem the other day again. As if the display card needs some warm up before it could display.
What would cause this problem?
OTOH, there is another problem that I am not sure if related, which I have been having for a while before this new display problem. If I shut down the PC for a short amount of time, the clock in OS would goes slower. If I shut it down for a long amount of time, upon start up the BIOS would do a countdown to ask me to load last config, something like that. And then the clock in OS would reset. It seems like it ran out of power to remember the time? What I know is that this problem started after I switched my display card with another PC. That battery was nearby to the PCIE slot so maybe I screwed up something.
It could be because the CMOS stores settings for Display setup as well as time/date and many other startup items. I would fix the battery problem first because it sounds like your CMOS is getting corrupted.