Laptop blacks out, but isn't in sleep mode

[DavidThompson]

My computer is an HP Pavilion Laptop 15-cs0xxx, running a 64-bit Windows 10 that I use for work and home life. Lately, if I leave it alone and open for too long, the screen will go black as though the computer's entering sleep mode, but the power button will remain lit up instead of blinking like it does during sleep mode or turning off entirely like it does when the computer "hibernates." When I attempt to reactivate the computer by moving the mouse or pressing keys, the display doesn't respond at all.

When I hold down the power button to turn the computer off, it succeeds, but when I turn it back on, after a brief display of technical information and a loading screen with the HP logo on it, the screen goes black again and the cursor is not visible. The bottom of the laptop also heats up during this time, and the fan becomes unusually loud. In most cases, after I've waited several minutes with the computer in this state, it does boot up normally but remains unusually slow and prone to freezing for several more minutes. In the most recent instance, it would not boot up normally for close to a half-hour, but after I cycled the power multiple times it not only booted up normally but wasn't even particularly slow.

I'm not sure if this detail is important, but during one of the recent failed boot-ups, I did see it appear to enter an ordinary sleep mode after being left alone for several minutes. The screen stayed black, but the power button changed from a constant light to a blinking one, as it does during sleep mode normally. Moving the mouse did end the sleep mode, but it only returned it to the same black screen.

I'm planning to purchase a back-up computer in case this issue persists, but I would still like to know if anyone has any suggestions regarding how to solve or at least cope with this problem. Thank you all for your time.

[WAWood]

@DavidThompson 

Win10 has enabled a new hibernation process known as Fast Startup -- which is enabled BY DEFAULT. This is different from Fast Boot, which is a BIOS/UEFI option.

Fast Startup is supposed to dramatically speed up the booting process, but in some PCs, it actually slows it down or causes it to hang. It's also a new form of hibernation known as hybrid sleep -- and this causes battery drain to maintain the state of the PC while turned off.

Disabling Fast Startup might fix booting and shutdown problems.

There are two ways to disable FastStartup in Win10: (1) through the Control Panel, and (2) through an elevated command prompt.

Control Panel - Open Control Panel --> Power Options.
Select "Choose what the power buttons do"
Select "Change settings that are currently unavailable"
At the bottom of the Window, under Shutdown settings, uncheck the box regarding fast startup

Elevated command prompt - run the following command:
REG ADD "HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\Power" /V HiberbootEnabled /T REG_dWORD /D 0 /F

In both cases, reboot Windows.

NOW, FastStartup is disabled.

See if that helps.