Sorry for your troubles well fix you up my friend. So let me get this straight, Windows 10 works properly? Just you can not get into BIOS and there is a valid POST just DEL key does nothing uh? Is this a new build? When did the problem start? I recommend grabbing a serial port keyboard or take your USB keyboard and plug it straight behind the motherboard. If still no go then plug the USB cable or another keyboard into a USB HUB if you have one if not perhaps a port behind your motheboard. Hit me back up when you have tried all these.💯🤷♂️✝
Let me answer!
Windows 10 works properly? Yes, perfectly fine from the first moment!
Is this a new build? Yeah, I changed MOBO but I could enter with my other one without problems
When did the problem start? From the beggining, the only way to access bios is clearing CMOS, that is the only way I can enter it
I use usb ports from behind also.
I noticed that I don´t get a POST , I just got a black screen, then w10 log in (but I disabled fastboot)
I use 2 monitors (in case this helps...)