Can't access BIOS after UEFI experiment

This Lenovo Thinkpad Edge E335 was originally supplied as a BIOS/MBR system with the ability to reconfigure as UEFI. Mainly out of curiosity I recently tried that and it worked fine, but having satisfied my curiosity I decided to revert to MBR. The process required a few BIOS settings to be reverted and worked fine - until I needed to access BIOS again!..I can now no longer interrupt the boot process with the Enter key to reset date/time, boot order, etc, etc and need an 'outside the box' solution to regain BIOS access. I have already tried killing all power and letting the BIOS reset itself but that hasn't worked, and tried booting with the hard disk removed. I have also tried every conceivable key combination, including Del and Shift F2, and am now out of ideas. Hope someone here has some!

BTW, I realise this isn't a Win 10 problem but came here as the site attracts many highly experienced guys and gals.

The key is F1 full details of how to enter the bios Recommended ways to enter BIOS - ThinkPad, ThinkCentre, ThinkStation - JP

How to Enter the BIOS on a Windows 10 PC | Laptop Mag

Thanks. The UEFI Firmware Settings option only appears when the system booted in UEFI. It doesn't appear if booted in BIOS/MBR, as this one did.

The MBR disk have nothing to do with you not able to access UEFI firmware settings. The MBR setting in UEFI tells the UEFI to disk you are using Master Boot Disk (MBR) this allows UEFI to boot the code on MBR disk (UEFI knows where to look for code on MBR disk.)

You can't reset UEFI firmware settings just by powering off your computer you have to take out CMOS battery or use jumper on motherboard.

3 Ways to Reset Your BIOS - wikiHow

FreeBooter said:

The MBR disk have nothing to do with you not able to access UEFI firmware settings. The MBR setting in UEFI tells the UEFI to disk you are using Master Boot Disk (MBR) this allows UEFI to boot the code on MBR disk (UEFI knows where to look for code on MBR disk.)
You can't reset UEFI firmware settings just by powering off your computer you have to take out CMOS battery or use jumper on motherboard.

I'm fully aware that MBR is not the issue and have already told you that I have removed all power (i.e. the CMOS battery and main battery) to try to reset the BIOS. Please don't put words in my mouth, I'm not a fool.

Please dont get abusive we are all work for free on here we dont need abuse we dont kno what knowledge people have so often have to give simple instructions