I know this thread is quite old, but recently I went through a similar problem, and I would like to share my solution, just in case anyone comes to this page (as I did) looking for help. Maybe I can help someone with my answer.
I have an Acer Aspire E 15 laptop. I managed to force it display its output to my HDMI monitor during boot by closing the lid right after pressing my laptop's power button. Then, my HDMI monitor showed the BIOS/UEFI splash screen.
More info here.