In the HP computer BIOS, the secure boot configuration is at >Advanced>Secure boot configuration. There are three options there.
If we are changing FROM option Legacy Support Disable and Secure Boot Enable we'll need to confirm by typing a 4 digit number presented.
Make sure the digits are echoed on the screen when you type them otherwise they will not be registered. This happened to me once when I use the numeric keypad without pressing the NumLock key. I tend to use the keyboard after that experience!