mac pro 5,1 missing operating system

[whimsica]

I have a macpro 5,1 with a sapphire graphics card (not the original card) It had a bootcamp partition and catalina installed. Somehow the catalina partition disappeared. I had to reformat the hard drive to start over. Now I get a

"missing operating system error"

On screen with a newly erased and mac journaled formatted drive. I made a high sierra osx bootable usb which was not recognized. And a bootable hard drive with high sierra, neither are recognized.

Holding down option does nothing, It also cannot startup in internet recovery -- nothing seems to get past this error, which someone told me was a microsoft error.

I also unplugged it for 30 seconds and pressed the power on switch and held it down. Not sure how to reset SMC on these older machines.

Is the sapphire card causing this problem? What can I try besides what I have already tried?

 

[rm5]

I recently had a problem where I did a botched upgrade from Big Sur to Monterey with OCLP. I have a Radeon Pro W5500 in my machine, which only supports Catalina and later, which obviously none of those OS versions are natively supported. I ended up with a completely unbootable system. Not your exact issue, but here's what I did, and what I'd recommend you try:

1. On a second Mac, create a High Sierra (or older) bootable USB installer
2. Get your hands on a Mac-flashed video card. You can get the Radeon HD 5770 that originally came with the machine for like $25 if you don't have one already
3. Put the said Mac-flashed card into the Mac Pro, hold down Option on boot to boot the installer
4. Run the installation of High Sierra (or whatever version you chose)
5. Create a USB installer for whatever version you want to install and put the other GPU back in

See if this works

 

[rm5]

Figured I'd add a few things, as I was running out of time when I was writing the previous post, so I had to write it quickly and thus missed some stuff:

• The reason why holding down Option "doesn't work" (it really does) is because the video card you're using is not Metal-supported. I'm imagining this is something like an RX 580 you've got in there? Once you put a Mac-flashed video card in there, you will be able to access the boot picker by holding Option.
• Internet Recovery is not supported on 5,1 Mac Pros (which really sucks) due to the firmware that they have.

You just need to follow the steps above to get back up and running again. Go and grab yourself a Mac-flashed card like the HD 5770 if you don't already have one. Then, you can just put the "new" card (the sapphire) back in and boot the system, and you're off to the races.

 

[whimsica]

That was it! I got my old video card installed and the option key started working again. I was able to install high sierra from a usb after clearing all the old partitions from the drive-- it didn't like it when the drive had extra partitions.

I didn't know internet recovery wouldn't work so thanks for the information also.

This was a huge help. Thanks.

 

[rm5]

Of course!! Glad it worked!