Used Macrium, now cannot get into system BIOS

I'm going to summarize where I'm at now. I never did say why I got into this mess with Macrium. I wanted to change my OS drive from MBR to GPT. The Windows MBR2GPT utility would not run, due to some obscure (to me) problem. So I decided to backup, wipe disk and repartition. After creating a Macrium repair "disk", but incorrectly writing is to C drive instead of USB drive ...

1. Started with seeing a Windows 8 style boot screen that gave me Windows 10 or Macrium. I could boot into Win 10, but booting Macrium resulted in simply black screen.
2. I never see BIOS messages from ASRock motherboard - you know, F2, F11, etc. I am unable to enter BIOS now.
3. Applied some advice about bcdedit. This got rid of Windows 8 style boot screen. Now computer boots straight to Windows 10 and never displays any choices.
4. Settings/Update/Recovery leads me to repair pages and option to boot into UEFI - but this only results in black screen.
5. I might have made a CSM change in BIOS the last time I ever saw the BIOS. Perhaps this is causing no video during boot? I attached a VGA cable, but still see only black during boot.

My best guess is that video is simply blocked/off during the boot process. After about 30 seconds I finally see the normal Windows 10 login screen. I can press F keys during boot time and then I never get to Windows login - so I suppose I am now in BIOS, but totally unable to interact with it!

So, I really can't do further maintenance or upgrade on this computer because I can't get into BIOS/UEFI settings! And I'm terrified of the idea of resetting BIOS - because if video remains blank after reset, then I'm lost.

I am unable to boot from any USB bootable stick - actually I don't know that is true, but all I see is black when I attempt to boot from stick.
So I burned to CD instead. I made a bootable CD with Macrium and another with WinPE. The Macrium CD didn't boot - actually I don't recall much CD drive activity. The WinPE CD sounded like it was booting - plenty of CD drive activity. But the screen remained black!
So I simply get black when using any repair media. And the screen remains black during "normal" boot and POST (I don't even know what POST is, but I know that it is part of the time before the Windows login appears). I'm fortunate that I do get to Windows login.
At this point it's looking like I need to reset BIOS.

Just a thought, since you have a laptop, there is the F7 key (on my laptop keyboard at least) that has an icon with laptop and monitor iconograph. Did you by any chance hit that key by mistake and have it send the monitor signal to an external monitor that's not connected? I'm just thinking out loud but having a black screen while in bios as well as during bootup sure sounds like this might be the case.

docGlenn said:

...the screen remains black during "normal" boot and POST (I don't even know what POST is, but I know that it is part of the time before the Windows login appears)...

Power On Self Test (POST)

Power-on self-test - Wikipedia

I finally reset CMOS by using the jumper on MB. That was fun, I haven't looked inside my computer for a few years.
So that restored video during boot and POST and I can once again access BIOS settings and boot into USB drives. I have no idea what went wrong that caused video to be blanked until the Windows login screen appeared.

docGlenn said:

I finally reset CMOS by using the jumper on MB. That was fun, I haven't looked inside my computer for a few years.
So that restored video during boot and POST and I can once again access BIOS settings and boot into USB drives. I have no idea what went wrong that caused video to be blanked until the Windows login screen appeared.

Well done! Now you know how to recover you may like to repeat your steps in post #1 to see if it was indeed Macrium that got you into this state, of if that was just a coincidence.