installing mojave on Mac Pro 5,1 with metal supported GPU NVIDIA GeForce GTX 780

I had that same experience on my 2010 5,1. Try this:

1. Shut down the computer.

2. Do a PRAM reset (hold Command, Option, P and R keys all at once as soon as your computer turns on--hold those keys until you hear it chime twice, then let go and let it boot up.

3. Power down the computer again.

4. Unplug the computer from your power source and wait a minute (SMC reset).

5. Plug the computer back in.

6. Press and hold the power button and hold it in until you hear the long tone--THEN KEEP HOLDING FOR ANOTHER 5 SECONDS.

7. The screen may go white and will appear that your computer is locked up. Just wait it out.

Let me know if this worked for you.

Aloha,

Keoni

I was having that exact same problem! I’m not sure what made the difference but it took me about four times before it kicked off and ran. At first, I only held the button until they saw the light flashing then let go. Since that didn’t work, I decided to hold the button until I heard the tone and then they go. But when that didn’t work, I held the button down and waited for the tone to sound all the way through and kept holding the button for past that tone. I would say keep trying to do it and with any luck you’ll be able to kick off the upgrade. Good luck, I feel your pain!

That's great news! I guess I should update my instructions to hold for 30 seconds past the tone 🙂

My DVD tray works fine, do I don't think it's Mojave. I know it's a long shot, but try using some canned air and blow out your keyboard keys, particularly the eject key. It could be a simple as that (or try another keyboard if you have one).

You can also force-eject by typing this in Terminal: drutil eject

Good luck, let us know how it goes.