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Trouble Installing Sierra on Mac Pro 5,1

Hi all, long term Mac user here with issues installing Sierra on a 2010 Mac Pro 5,1.

System Specs: Mac Pro (Mid 2010), 2.8 Quad-core Xeon, 32gig Ram, AMD Radeon HD7xxx 3072mb Graphics, Yosemite (latest).

So here's the issue. I'm trying to do a clean install of Sierra on a seperate drive.

No problem doing the install & all the updates...but if I boot back into my Yosemite partition, the Mac no longer recognises my Sierra drive as being bootable . It no longer shows up as a boot option when I look under system prefs/Startup disk..

Ive tried this a bunch of different ways...using SSD's vs Spinning disk. Internally mounted vs Firewire SATA caddy, & also clean install vs Clone-then-upgrade. I always makes sure the disk is GUID formatted.

Always the same result. Sierra installs just fine, & pulls down all the latest updates.....but if I power down the mac, then restart...or simply reboot to another system....then the Mac *cannot* see the Sierra partition as bootable.....If however I take this new sierra drive & attach it to my 2011 Macbook Pro (running Sierra already) it sees it just fine & will boot from it.

Ive tried booting the Mac Pro with 'alt held down', & it doesn't bring up the 'startup disk selection' screen as expected. It just never boots.

Ive changed the pram battery. No difference....so pretty much i'm out of ideas now. Ive had almost a dozen macs over the years, & am an old hand at cloning, upgrading & installing systems, & have never come across an issue like this before.

Can anyone help?

Kind regards

Ru

最后更新：2017-09-25 04:20:31

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