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Thanks - I've tried (a) several times - it restarts but does not get as far as either BIOS or Windows - just a blank display. I need to hit the reset button after 10-15 minutes and then it will boot back into Windows.
I've been hitting the DEL key repeatedly every time it boots, but it has never been recognised. Windows seems to be locked into a fast startup mode that I can't break out of (even though I have the "fast startup" option disabled.
So EFI is there and some motherboards boot into BIOS when the system drive is unplugged. Or remove CMOS battery and try and try and ...
As I think Pentagon suggested, try removing/disconnecting the system disk, then see if you can acess your BIOS/UEFI.
How is your keyboard connected?
I'd unplug the drive, start the machine which will now be in the BIOS, configure as needed then hot plug the drive and reboot.
During POST press Del to enter BIOS or F12 to launch boot menu that has an option to enter BIOS.
If everything fails, reset BIOS by taking out the BIOS battery (CR2032)
I'm guessing the keyboard isn't 'seen' during POST.I've been hitting the DEL key repeatedly every time it boots, but it has never been recognised.
Before converting the mbr to gpt disk, could you enter the bios?
There are settings to change in the bios to make it uefi, so you need to now that the System disk is gpt, change the bios settings to full uefi. Disconnecting the disk may be a solution to change the settings in the bios.
Disabled legacy bios, csm among others
Do you have an old PS/2 keyboard? Or can you use the black USB-Port on the rear/backside?
My original BIOS had a Fast Boot option. In this option BIOS USB drivers weren't loaded making a boot some seconds faster. Once set, you don't have USB during POST and consequently no mouse or keyboard. The only way was to reset BIOS.
Newer BIOS versions doesn't have a Fast Boot option.
That is why I suggest a BIOS reset as last option.
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