SPCR

I have a 15" laptop and a 27 inch monitor, which is connected to the laptop via HDMI.
I never use laptop's monitor, although it's an excellent IPS screen. However, every time I turn on the laptop, I have to setup the multiple display all over again!

Display-settings-->use only this monitor, so the laptop monitor is always turned off when the lid is down.

Why can't Windows 10 save these settings??

Everything that can be updated has been updated.

Does using the options presented by pressing the Windows key and P make any difference?

It's set to PC screen only. I'll see later when I turn it off if it makes any difference.

It doesn't change anything.

I guess every time I turn on that laptop connected to that monitor I'll have to set up the large monitor as the only screen.

I suppose everyone is doing this..

Have you looked in to BIOS/UEFI options, see if there is anything about external screen settings?
I mention it as I noticed a setting on some older Toshiba laptops I was working on but didn't pay it any attention at the time to see what options were / did.

Regards,
Seb

Unfortunately, I can't access BIOS.

It was suppose to be fn+F2 for Lenovo Ideapad Lenovo 510-15ISK, but it doesn't work.