Trouble Upgrading from El Capitan 10.11.3 to High Sierra.....

Well, I got it done! I'm now running the latest version of High Sierra. It took a little doing, though. First, I didn't have the original video card that came with the computer. I'd purchased it used and it came with a GeForce GTX 680. I thought it was the Mac Editin, but more on that later.

So so I found an original video card on eBay, bought it, and installed it. I also removed the three extra drives I had in the computer and disconnected all external drives. Then the firmware update for booting went fine and so did the install of High Sierra. I went with the 10.13.6 install because it had the proper firmware.

I then did some other software and security updates. But iTunes would still not recognize my new iPhone SE. However, I found a thread where someone else had the same problem. I downloaded an earlier version of iTunes, installed it, it searched for some new stuff, and when it was done, I now had an updated version of the latest iTunes and my new phone was recognized. I then restored the new iPhone with the backup from my old 5S and all was good. I also ran a new backup of my hard drive, using Carbon Copy Cloaner.

Now onto Mojave. As it turned out, my video card did not say Mac Edition on it. Rather than risk trying to flash it, I opted to buy yet another video card from eBay. It arrives on the first of July. Once I get that, I'll still need a new Bluetooth/network card. Then I can take the computer to Mojave. I'm hoping that will last me awhile.

And thanks to all for their help!

So, in my reading online, I'm finding that I need a firmware upgrade to install High Sierra. I have Boot ROM Version MP51.007F.B03 and I need MP51.0089.B00 at a minimum for High Sierra. Problem is, it also requires the original video card to install the firmware and I don't think I have that. Does anyone have some solutions?

I got the information here:

https://forums.macrumors.com/threads/mp5-1-what-you-have-to-do-to-upgrade-to-mojave-bootrom-upgrade-instructions-thread.2142418/

and here:

https://www.usedmacs.us/?name=How-to-Upgrade-the-Mac-Pro-5,1-to-the-latest-firmware-and-Boot-ROM-Version&art=how_to_mac_pro_firmware_upgrade

That link takes me to a page that says High Sierra, but when you click on "Open", it says Mojave and you have no options beyond closing the window.

Yes, my Mac Pro is completely compatible through Mojave at least. It's the last generation Mac Pro and is loaded with RAM and hard drive space.

All my data is backed up on a daily basis using clones of my hard drives made with Carbon Copy Cloaner.

I got a warning from some source to upgrade to High Sierra first before going to Mojave.

I have another problem. My Model identifier is MacPro5,1. And the Boot ROM Version is MP51.007F.B03. I'm thinking I have the latest firmware already, but when I try to do an install, the screen essentially stops at the part where it says to shut down the computer and then hold the power button in until I get the tone. I was able to do that successfully once, but now it's asking to do it again and I can't get past the shut down because it no longer works. What's going on?

And do I have to be in the administrator logon to do the upgrade, or can I do it from my personal logon and still get the upgrade to work? The computer was originally my wife's, but she no longer uses it.

I meant a newer version of iTunes. But in any case, I can't seem to upgrade to High Sierra. I even tried upgrading to just plain old Sierra and that didn't work either.

Don't see how that would make a difference but I'll download 10.13 again and try opening the installer from there.

OK, I believe I got a successful download of High Sierra. However, it says I need a firmware update. I presume the power button is the one on the tower?