Thanks for your reply - but I've already tried that. When I tap "ESC" on startup I get a menu list and on choosing F9 the notebook displays the Boot Manager screen (a grey screen with Boot Manager in a blue section at the top).
In the grey area it says;
Boot Option Menu
"up and down arrow symbols" to change option, ENTER to select an option.
Press F10 to BIOS Setup Options, ESC to exit.
That's it, there's nothing else. If I press F10 it just goes to the standard Main/Security/System Configuration/ Exit screen, the System Configuration option takes me to Boot Options and the UEFI Boot Order - which doesn't accept the USB Memory Stick - so I'm back to the original problem............................ It looks like this notebook is now defunct!