MacPro early 2009 (4.1) can't/doesn't want to boot

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MacPro early 2009 (4.1) can't/doesn't want to boot

This Mac is special — I have a Mac Pro Early 2009 with dual CPUs. It boots, but only when it feels like it.

A few months ago, I figured out why it wasn’t starting: a component was shorting everything. After removing that part, it finally booted.

Yesterday, I tried to boot it again to install the latest supported macOS (El Capitan). I managed to update one of the systems, but the second one wouldn’t boot (i have two MacPro). To troubleshoot, I disassembled the machine and tested the parts outside the case, plugging the main board into the processor board with the PSU. Nothing happened.

Feeling disappointed, I reassembled everything back into the case — and it booted! But now, once again, it refuses to boot. I don’t want to keep disassembling and reassembling it, hoping it will eventually work.

What worries me most is the PSU: it makes a whistling or high-pitched noise, almost like it’s charging up to handle the boot sequence. It seems odd that the PSU could be failing, since yesterday I was able to restart the Mac multiple times without issue.

So I need help deciding: should I just buy a replacement PSU on eBay for about €100 (~$117–120), or should I keep investigating other possible causes?

For context, here’s what I’ve already tried:

Resetting the BIOS, PGOOD, SYS, and SMC using the pins on the main board
Reseating each RAM stick
Reseating the two CPUs on the processor board
Reconnecting every cable

I’d appreciate any advice on what to do next.

Mac Pro, OS X 10.11

Posted on Sep 29, 2025 9:30 AM

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Answer 1

Top-ranking reply

Grant Bennet-Alder

Level 10

139,799 points

Sep 30, 2025 11:18 AM in response to UnVeluX

There are some LEDS on the backplane board that show whether voltages are OK. Towards the left side, just over halfway up. Standby power is an always-on power supply that MUST be present to allow staring up.

The approved method for your debugging is almost exactly what you did before. That is, remove everything in a slot, including all drives and DVD readers and PCIe slot cards, and go for the Chime. Then add back one item at a time, and when it fails, it's the last component you added.

Are you getting any "help me" codes from the power-on indicator light?

What graphics card are you using?

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Answer 2

Sep 30, 2025 2:55 PM in response to UnVeluX

That tells you the overtemp lamp test circuit is working, and it has the standby power needed to start up from the button.

if the [12 Volt powered] fans won't go even with no cards in slots and no drives connected, it very well may be the power supply.

I would suggest you try swapping the CPU tray with the other machine to make sure it seems to be working.

It would also tell you all your Error-correcting RAM is working (or not). If that works, there is not much else that can go wrong except the power supply.

If you want to be certain, you could swap your known-good power supply into the dead machine. It seems onerous, but the cable harnesses are fairly well-behaved and it does not take that long. Or you could swap the suspect power supply into the otherwise known-good machine. If the problems follow the power supply, you know it's bad.

¿Which would require the fewest swaps or the shortest downtime?

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Answer 3

Sep 29, 2025 10:12 AM in response to UnVeluX

Does the non-recharging 3.00 Volt coin cell long life lithium battery (half-hidden behind the graphics card slot) still have OVER 3.00 Volts when measured in your hand?

Use a very bright light and understand fully when removing -- breaking the holder WILL ruin your afternoon.

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Answer 4

UnVeluX Author

Level 1

4 points

Sep 29, 2025 10:26 AM in response to Grant Bennet-Alder

WOW, i got new info, seem like the bottom PCIe slot was faulty. After unpluging the graphics card it boot instantly, i replug it in the second x16 slot in the middle and still boot. And yea, the cell is still 3.5 volt even 2 years after replacing. I will not close this post, i case tomorrow it dose the same. So i keep u updated if anythign happend !

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Answer 5

UnVeluX Author

Level 1

4 points

Oct 2, 2025 9:26 AM in response to Grant Bennet-Alder

Sry i got delayed, But I swap the CPU tray, the HDD and graphics card in the good macpro, and everythink works fine, so it's a fcking PSU issues. I will try to get in the psu and see which components is damage. Unless if u have an other idea, why it could be bad.

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Answer 6

Sep 29, 2025 9:34 AM in response to UnVeluX

when it "does not boot" what are the EXACT symptoms presented?

fans on or Not?

chime or not?

power indicator light off, on solid, flashing a code?

display light up on not?

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Answer 7

Oct 2, 2025 10:27 AM in response to UnVeluX

If it is the power supply, you said 100 Euros gets you a working one and hopefully a working computer, and you can repair the old one at your leisure and sell the repaired one the used market when fixed.

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Answer 8

Sep 30, 2025 12:13 PM in response to UnVeluX

if the fans turn on, but no progress, any "help-me" codes are blinked in the MAIN power indicator, or the OUTSIDE front of the unit.

The GT120 card does not use any Aux power cords, which makes things simpler. That card could also be placed in ANY PCIe slot -- it will just run slower in the top slots, but it will happily run.

[Edited by Moderator]

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Answer 9

UnVeluX Author

Level 1

4 points

Sep 29, 2025 9:52 AM in response to Grant Bennet-Alder

nothing, the diag led power, up the two red also when plug the cord in, but after clicking the power button, no chime, no fan, no power indicatior, the power button stay off, even when shorting the pin on the mobo

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Answer 10

UnVeluX Author

Level 1

4 points

Sep 30, 2025 11:46 AM in response to Grant Bennet-Alder

GPU : Nvidia GT120 (A1310) The original.

And I'm a little bit misunderstanding u about the LED. I have the diag LED, but that's all. ( Only the 5V lights up, which is good)

are u talking about the one right next to the diag button for the sys pg, efi done and gpu ok ?

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Answer 11

UnVeluX Author

Level 1

4 points

Oct 2, 2025 10:52 AM in response to Grant Bennet-Alder

on what market can i sell it ? cause i've look for old one HS for part and oftenly there where only old ads or very costly. So idk if it will sell fast. And the spec (6Gigs DDR3 2x2.26) could playign against me.

But i'm happy to try, so what du you recommend ?

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Answer 12

UnVeluX Author

Level 1

4 points

Oct 2, 2025 1:49 PM in response to Grant Bennet-Alder

Oooh, U meant the PSU, but why sell a broken or very badly one ? And i was thinking about transforming the mac into a real PC, transforming the psu by replacing the internals and putting inside a mini-atx or ITX and re-routing the graphic card PCIe lane and IO of the case to the main board. If i don't wana replace the PSU. but doign a pc inside woudl be in some time. But im thinking about it now that ik that the PSU is faulty

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Answer 13

UnVeluX Author

Level 1

4 points

Sep 30, 2025 10:04 AM in response to Grant Bennet-Alder

Well, it's broken (again). I'm starting to feel it's a PSU issue, but how can i prove it?

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Answer 14

UnVeluX Author

Level 1

4 points

Sep 30, 2025 12:22 PM in response to Grant Bennet-Alder

Everything on this page is already OK, i check the entire manual, each time it doesn't give me a reason why it doesn't work, the 5v lights up and the two red led lights also up when plug and unplug

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Answer 15

UnVeluX Author

Level 1

4 points

Sep 30, 2025 9:59 PM in response to Grant Bennet-Alder

I will try swapping the CPU tray, and if this works fine i will try the PSU swap. I tell u more at around 19h UTC+1, so around 13h for u or 1pm, if ur from the US

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