I just had this problem whereby whenever started up my computer the display would be blank until the Operating System had fully loaded. After it did, it showed the Lock Screen. I would be unable to see or enter the BIOS, the splash screen (in my case, ASRock) would not show as well. However, when my OS loads the display recognises it and then appears.
How do you fix this problem from happening?
Well, the reason it does that is because in the BIOS there is an option of whether to set the Primary Boot to the "PCI-E slot" or "Integrated" (forgot what it was called so let's say Integrated). If it, by some chance, switches to Integrated then you have the problem of it not displaying the Splash screen, BIOS etc... and you probably can't access the BIOS anyway to fix it.
Now, if you have multiple GPUs connected to PCI and/or you have a CPU with an integrated GPU then, if by some chance you have this problem, all you have to do is switch where the display port is connected to, to something else. Then, if you reboot your computer it should come up with the Splash screen and the BIOS hotkeys (usually it says F2). Afterwards, you just need to enter the BIOS and switch the primary boot, if you have an integrated GPU and a dedicated GPU, from Integrated to PCI-E.