Is the monitor attached to the GPU? you haven't attached it to motherboard instead?
On another PC, download the
Windows 10 media creation tool and use it to make a win 10 installer on USB - as suggested already.
You can install win 10 without a licence. When you reach the screen asking for licence, click "I don't have a key" and win 10 will continue to install and once you get a licence key, you can go to settings/update & security/activation and enter the key there.
You shouldn't need to go into BIOS before installing on a brand new motherboard, it should be set up to boot off a USB/DVD without you needing to change anything.
You seem to have enough help in here, it sounds like you need actual help there (in person). I know I did the first time.