Odd BIOS behaviour on a Edge 330 motherboard

[clabr]

Recently replaced my faulty motherboard with a new one (bought it from ebay).

At first everything seemed as it should.

The Boot Menu and Application Menu appeared as they should. The App Menu with all the normal entries (Lenovo Diagnostics, Setup)
Also with the option (entry) to enter Intel AMT with Ctrl+P (which is what interest me the most)

Then I have reinstalled the wireless card and the HDD and booted to Win 10.

At first the the option to interrupt bios with Enter key was working.
But then after a few windows boots:

I cannot interrupt with Enter (option is enabled in bios)
I cannot enter bios with F1 (only from Win10->recovery->firmware setting)
I cannot reach the Boot Menu if I don't remove the HDD

When I get to Menu, there are no entries in App Menu anymore (no option to configure Intel AMT).
Why did this disappear I cannot understand?

In BIOS all I remember to change was boot order and enable Secure Boot.
Intel AMT, Computrace are enabled and not activated.

I tried loading Bios defaults, removing CMOS battery (all it changes is the Real time clock is reset; all other options in bios are kept; no defults are loaded etc)

In BIOS the "system board serial number" appears as INVALID. The "system unit serial number" is OK though.
I have checked it on Lenovo site:
The board is out of warranty (warranty was 1year; a board from a 2012 Thinkpad bought in Croatia)

I would like to have the App Menu entries back, and option to enter and configure Intel AMT
Also to be able to interrupt boot with Enter.

Thank You.