I just installed an Intel i9-9900k on the ROG Maximus XI Hero. Windows is installed on my 250gig Samsung Evo SSD, but now I can't boot to windows unless I do it through the BIOS. Is there some setting I'm missing, or do I need to re-install Windows?
Just run the media creation tool from microsoft (it will download the W10 installation pgm) , and choose what kind of media you want to use; flash drive or disk. When finished, boot using the new flash drive/disk and follow the instructions.
FYI, I think the OP's problem was with Fast Startup. If Fast Startup fails his computer won't boot, but if he enters the BIOS first, his computer will boot without Fast Startup (probably to allow any changes to take hold) and his computer boots successfully.