Few things that come to my mind:
 
Are you getting any beeps?
 
Are you using dedicated video card or not?
 
How old is your CR2032 battery and have you tried brand new one?

The setup has a dedicated graphics card and I can see the memory checking screen go before it gets to the checksum error and asks me to press F1 or the DEL key.
 
Therefore, I get the single beep, as to when it starts displaying output to the screen.

The CR2032 battery is less than a year old.

If I repeatedly press the DEL key, I can get the motherboard to freeze at the memory checking stage. Or if I press ESC, to bypass the memory check, once again the motherboard freezes.

The computer was working prior and after I inserted a PCIE card containing an M2 SSD, I read online that I needed to make a setting change within the BIOS in order for it to be seen within Linux. However, I failed to get into the BIOS and after a couple of attempts and instead of pressing the power button on the motherboard, I it the RESET CMOS button instead. This obviously meant that I had no chance of getting the computer to boot into Linux till I am able to get into the BIOS screen.

If I don't have a keyboard connected, the motherboard tells me so, before if I do, the message goes away but then the computer freezes when a button is pressed. This is checked by several keyboards, all USB and using a combination of them and a PS2 to USB adapter.

I cannot say for certain whether or not it all started after the insertion of the PCIE card, since I have had no reason to enter the BIOS setup screen for the last 8 months (when I replaced the battery and added 24GB of memory). 

I've since taken the card out, bearing in mind that the computer did boot and work after the card was inserted, removed the CMOS battery and left the computer unplugged for over 18 hours. I did, before plugging it back in again and putting the battery back in, press the ON button to make sure there was no residual power.

Having worked on computers for longer than I dare to remember, both building, fixing and coding them, I cannot remember coming across such a problem. The only thing I don't have is a native PS2 keyboard, but in this instance, not sure if that would make a difference (as I used the PS2 - USB adapter originally to restore the BIOS).

The motherboard currently only has the bare minimum required in order to boot, that is two memory stick and a graphics card (it has no internal graphics chip). Everything else has been disconnected, that is the SATA cables, USB expansion cables and the front panel audio cables.

It is unusual not to be able to get into the BIOS setup screen, a right royal pain in the rear, as I know, once I do, everything should work as before. 

Could the BIOS be corrupted, such that it prevents entering the setup screen? How can you tell or find out.

I cannot see how the video card would prevent the motherboard from going into the BIOS screen, even if it didn't update surely the 2 7 segment displays would indicate that it was no longer waiting for user input and advance from 7F?

I'm now regretting trying to get into the BIOS screen on this motherboard, should have left it well alone. 

But eventually something would have caused the need, better now than when I really need the computer.

It says in you don't have video, so I'm ruling that out as well.
 

If you do not have video and are getting these POST codes, It would most likely be that the video card in your system is not functioning.

 
Will the board boot with only 1 stick of ram?

when I replaced the battery and added 24GB of memory).

 
Was this all new ram or did you add to existing setup?

I sent the member a PM to see if the member has any additional info.