HP Pavilion shuts down after being in sleep mode for approximately 3 hours

[Nanindesmoines]

I am sorry if this is not the correct board for my question since I don't have a clue what it would fall under. My laptop had a new motherboard put in because it was doing random shutdowns where I would lose whatever I was working on when I booted back up. I have it back from the warranty repair and it is still doing it but in a different way. It goes into sleep mode for a while and then shuts down. When I power back on my sign-in window presents its self, I click on it and all the tabs come back just the way I left them before It powered off (a good thing). This happens regardless if it is plugged into the power adaptor or running on a full battery. Is there some hidden hibernation thing that happens? I checked to see if it is set up to hibernate and it is not.  Besides, if it was hibernating would I have to click on the sign in to get back in? It is just so annoying to have to power back on and sigh in because it won't stay in sleep mode. If anyone can explain to this Grandma who has no techies in the family what might be the problem It would make my day!!!   

[WAWood]

@Nanindesmoines 

YES -- the new hidden hibernation thing is known as Fast Startup.

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.