How to enable Windows 10 to be put to sleep?

I'd like to be able to use the Sleep option ["The PC stays on but uses low power. Apps stay open so when the PC wakes up, you're instantly back to where you left off."] in Windows 10. However, when I click on Sleep, the screen goes black, but everything else [case fans, etc.] is still running. If I then move the mouse, the screen comes back on, and if I select Sleep again from the menu, my computer appears to go into a proper sleep. But I don't want Sleep to be a two-step process.

Moreover, my machine also appears to be unable to wake up from sleep. When I press the blinking power button to wake it up from sleep, the screen remains permanently black. The code on the motherboard indicates "System is waking up from S3 sleep state", but it never does wake up. It just stays in that "waking up" state with a black screen. My only recourse is to do a hard reset. Not ideal.

So, how do I enable Windows 10 to go to sleep [with one press of the Sleep option, and to wake up]?

To be clear, in the Power Options control panel, I have selected a custom power plan as my default, and one of the settings in there is "Sleep after: Never". I have it set that way because I don't want my PC to go to sleep by itself, ever. But I do want to be able to tell it to go to sleep. Maybe that's my problem: it can't be set to never sleep, and then be put to sleep? I don't know. It seems like that should be possible, but maybe it isn't?

Otherwise, there may additionally be settings in the BIOS that need to be enabled [or disabled] in order to allow the computer to sleep in the CPU Power Management Configuration. I'm not sure about those.

Thanks for any info / advice.

Weird situation with sleep not working at first, then working on the second try. I have no particular idea about that, but regardless it would probably be worthwhile to run "powercfg -requests" to see if there are devices or processes that are preventing entering sleep.