You might need to go back to onboard graphics to go into the bios to update the bios. But first check the website of the mobo manufacturer to see if there is a more recent bios to download.
I'd also try resetting back to defaults or even a doing a CMOS reset (worse case).
Before all that, have you tried a few cold starts? Ie, power off at the wall, press the on button, turn back on at the wall and boot up? Repeat a few times.
I had a mobo before that reacted badly to GPU changes. I'm still unsure what process I had to use to get it working but remember trying all of the above at some point then it'd suddenly would start working. Think is was a Gigabyte z77 board with a 3770K installed. Once it worked, all was fine until the next GPU upgrade
could have course be a faulty gpu.