Before upgrading to High Sierra, check your drives

[Joe]

Is the keyboard it is using wireless or USB? Whichever it is try the other kind to see if you can get it to recognize startup keys.

[Ear]

Good idea. It is wired but I suppose the USB controller could be having a problem too.

I'll try a couple different keyboards... wireless and an older wired one.

[Joe]

Also clear the NVRAM. If USB goes wonky that can fix it.

[Ear]

Isn't NVRAM the new PRAM? I think the key combo is the same.

[Joe]

Oops...NVRAM and PRAM are the same. What I meant on the last post should have said:

How to reset the System Management Controller (SMC) on your Mac

How to reset the SMC on Mac desktop computers

Follow these steps for iMac, Mac mini, Mac Pro, and Xserve.
Shut down your Mac.
Unplug the power cord.
Wait 15 seconds.
Plug the power cord back in.
Wait five seconds, then press the power button to turn on your Mac.

[Ear]

Yep. I tried the SMC trick too. 

I'm thinking the PRAM was holding onto the initialization info and it got wiped. I think the boot volume gets locked once the install starts, so it needs to get that info from the PRAM (NVRAM). It got zapped and now it doesn't know what to do.

[Joe]

Yep. I tried the SMC trick too.

I'm thinking the PRAM was holding onto the initialization info and it got wiped. I think the boot volume gets locked once the install starts, so it needs to get that info from the PRAM (NVRAM). It got zapped and now it doesn't know what to do.

Well if you can get the drive out and format it and stick it back in and it still does it I would say the firmware has been hosed. I would still try a different keyboard type first though.

[Ear]

... and if the firmware gets hosed, is it a paper weight? Or do you know of a way to fix the Firmware? Is Firmware stored in the Logic board?

[Ear]

I just looked up Firmware restore... plenty of info on that too. 

I'll try the keyboard, target disk, etc... then remove the drive, if that fails... I'll mess with firmware last, if nothing else works.

[Ear]

... if the Firmware is bricked, I wonder if I can get it to boot with an external Linux system, like Ubuntu, then designate my external MacOS as start-disk? Wouldn't a standalone Linux have its own Firmware and Kernels?

[Joe]

... if the Firmware is bricked, I wonder if I can get it to boot with an external Linux system, like Ubuntu, then designate my external MacOS as start-disk? Wouldn't a standalone Linux have its own Firmware and Kernels?

Firmware is hardware on the board. Not sure if there was a way to restore it. I know every now and then Apple has firmware updates. When you apply it, it reboots and does some hidden command line things to it to update the firmware. But if you can't get it to boot I am not sure if you can restore it or not.

To get it to boot from any other OS it has to get through the firmware before it can recognize keyboard commands which you have to do in order to boot from another external. You would be in the same boat you are in now with trying to boot OS X from your external. The mac can't get to it.

[DigiCorn]

I've successfully booted "dead" G5s and older from an external DVD-ROM Firewire connected drive. It won't work via USB, and you have to have an actual OS install disk. No idea if this would work on newer machines via the Lightning plug.