The Mac Pro First Generation is an Intel Xeon-based workstation computer manufactured by Apple Inc. The first generation model includes the machines from 2006 through 2008.

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Mac Pro 1,1 A1186 will boot and sleep, but not restart.

MacPro Original A1186 Dual-Core Intel Xeon

Diagnostic LEDs reflect no issue and the Mac is working fine until needing to restart rather than shutting down.

When restarting, as the mac powers down, there's a click from the optical drive resetting as the power cycles and it's here where it gets stuck - right before powering back up. At the same time the optical drives click, Diagnostic LEDs 2 & 3 flash briefly & the process repeats as the power cycles trying to restart.

Pressing the System reset switch doesn't yield a restart, rather inducing the problem and getting stuck. Strangely, getting stuck by way of the System reset switch results in a brief flash from Diagnostic LED 7 immediately after the flash from LEDs 2 & 3 which doesn't happen when simply restarting.

Removing the optical drives only quiet the issue as there are no drives to click, only Diagnostic LEDs 2 & 3 to flash. Apple Hardware Test returns no errors / have reset SMC / unable to zap PRAM.

Everything I can find online relates to fixing booting and start up issues, which all check out fine, including sleep. It's as though when restarting, the process isn't completing the power down or something drags and interferes with the powering back up.

Any help would be appreciated.

Answered! View the answer I have this problem too

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What OS X are you running? Do you have another boot drive in it?

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Deck the Halls
With tools and Fix Kits

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Resolved: Bad Memory Modules Installed.

This makes the second time I've bought and installed bad RAM. After removing the recently installed memory I've been restarting without issue.

Initially four of the six DIMM risers with memory installed were showing as being empty. Troubleshooting, I tried moving memory, by pair, switching order, and between cards. I was surprised at the results. A pair could return an error led pending the slot yet be fine in the same place on the other card, or if their order was reversed. Also surprising was the fluctuation of memory recognized - even with two (a pair) of 4 GB modules returning between 1 GB and and 8 GB.

Unable to fix the situation, I replaced the memory with 6 new 2 GB modules. "About this Mac/System Report/Memory" recognized them so I assumed they were fine. Following a suggestion I tried removing them and it's as though I've got a new computer and have no issues. All the troubleshooting I did trying to fix it has paid off.

I'd still like to up my memory but since I've tried twice now, both times supposedly with "Apple Approved" and for my model, I'm a bit leery.

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I'm glad you managed to sort the restart issue out. In fact, I inclined to think there were more than one issues there, maybe you were actually having more than one problem that added up.

Mine had RAM upgraded – changed 512 + 1G modules to 2GB modules), battery changed and FW upgraded, and then only the problems stopped. Maybe that's a combo :)

For the RAM expansion issue, I had similar problems when using different brands at the same time. I ended up buying a lot of paired HP server RAM modules and that went well...

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The battery was going to be my next bet.

For me, the exact same behaviour was a firmware issue as I had a Mac Pro 1,1 CTO and the firmware revision I had was somewhat special (higher version as the last released HW revision). I did a firmware upgrade to the Mac Pro 2,1 firmware and that solved the issue altogether.

However, before doing that and getting rid of this problem, I changed the battery and it turned out that changing the battery momentarily solved the issue for 1-2 restarts, then the problem came back. I swapped cards, removed cards, tried out all kinds of things.... the FW upgrade solved it.

Actually downgrading the firmware a step would have also solved it probably, but it was not possible.

Update (05/07/2017)

How are you unable to zap the PRAM?

Power on, then immediately hold the alt-command-p-r keys...

Oh, a thought. Plug your keyboard directly into the machine, don't go through a hub or a usb card!

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I know - strange, but when you zap the PRAM , the machine sounds as though it's powering down briefly, the same as when you restart. And that's when it gets caught.

Keyboard is plugged into the back of the display but I forgot about that and a good suggestion.

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Peter will be eternally grateful.
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