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MP 6,1 6.1 Boot Loop Help!

S

sofreshsofoul

macrumors newbie
Original poster
Dec 14, 2025
8
0
HELP!!! Mac Pro 6.1 Boot Loop

I’ve replaced both the GPU and Processor, same issue..

Cannot boot into recovery mode or safe mode via keyboard commands, my next thought/step is to reapply thermal paste to the chipboards/replace the system battery.

Any thoughts/ideas???

Thank You! Any constructive input is highly appreciated!
 
I’ve never successfully gotten this to boot it’s a university surplus so they pull the hard drives before they sell them. I put a hard drive in there from an old 2015~ MBA.
 
Have you tried reinstalling the macOS system on that borrowed drive?
If not, I think your best first step is to try booting to an external bootable installer.
Download a good choice for a system to install. Latest would be Monterey (macOS 12).
You can do this from another Mac. There's a variety of methods to get that bootable USB installer, pretty easy to search.
Download the installer app, then use that app to make an bootable external USB, using the terminal.
Boot your MP 6,1 with that installer, follow the steps to reinstall macOS. That should get you going again (assuming there's not a hardware problem of some kind, and you just need a correctly working system
 
Hold the Option key while booting. The firmware boot selector should come up, allowing you to choose the USB volume. Sounds like you're defaulting to the internal drive, hence the boot loop.

I agree with DeltaMac - the most obvious cause is an incompatible OS install. Install anew, and see what happens.

I'd probably go even more cautious. I'd use an external USB installer, and install to an external drive. Ignoring the internal drive for the moment. That eliminates it as a question mark, allowing you to confirm the rest of the Mac works.

Once you get your 6,1 booting from an external drive, then try installing to the internal drive. See if that goes well.
 
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What macOS system do you have on that "boot USB"?
That is just a system installer, and NOT a bootable full system, correct?

And, yes, absolutely hold your Option key when booting, so you can make sure to select your external bootable installer.
 
Tried holding the option key. Doesn't do anything. Have boot USB, no response. Can try another hard drive. Mavericks is on a boot USB, should be a fully bootable system as far as I know.
 
Mactracker says the 6,1 first shipped with Mavericks, but I seem to recall nvme compatibility was added with Sierra (Apple nvme) and High Sierra (3rd party nvme drives). I suggest trying to boot and/or install with High Sierra or later.

You might also try unplugging the SSD you installed internally. It may be incompatible, or defective. A bad internal drive can hang boot attempts. You should be able to boot from an external drive even if there is no internal drive. Useful for diagnosing problems, like boot issues.
 
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