iMac (early 2009) won't power on and emits a buzzing noise

What is the cause of this problem?

Most likely, its power supply has failed.

Is it fixable?

Yes. Used power supplies are inexpensive, but they are equally old and equally prone to failure.

Comment: Your initial description "when I plug it in" implies the Mac is often left disconnected from utility power, or that it may have been disconnected for a prolonged period of time. That practice is not conducive to longevity. All desktop Macs should be connected to power whenever practicable.

KiltedTim wrote:

I would think if the issue was the hard drive not spinning up, you'd get an error message indicating a failure to boot. Failed hard drive doesn't seem to fit with the symptoms as outlined in my experience.

"after a long time of being plugged in (which seem to get longer each time) the electric noise stops and then I am able to power on the device"

I have encountered a fair number of Hard Drives which have "buzzing" noises which can sound like a bad fan bearing, or even marbles rattling in a can (yes that loud), buzzing, screeching, and even a few other sounds.

I have also seen a fair number of Hard Drives fail to such an extent that it will prevent anything from being displayed on the screen....never even see the flashing folder with the question mark. Yes, some failing drives can lock the system up that it never gets far enough to display anything on screen (or perhaps I never gave it enough of a chance to time out & display the blinking folder....I think I gave one at least 5 minutes).

Hard Drive failures are the number one failure with those older iMacs. Power Supplies were the second most common failures.....usually due to the large capacitor bulging & leaking.

It all depends whether "able to power on the device" means there was no power on at all.....however, most users cannot notice the subtle signs when there is no video on screen. I see users use "power on" and "booting" interchangeably.

I actually was thinking bad power supply at first until I read more of the OP's post where the other symptoms & behavior combined sounded more like symptoms of a Hard Drive failure to me. Typically there will be just one part failure, but with such an old system....especially if it has not been used for a while, it could have multiple failures. And it sounds like the OP just acquired this iMac so there is no background history. Usually you are buying other people's problems when you buy something used (may be Ok if you are skilled at fixing things & have access to the necessary items to fix it on a budget).

Unfortunately we will probably never know the answer here.

Tom_Tom1 wrote:

The problem was the power supply, thanks everyone!

Thanks for the update.

Congrats @KiltedTim on calling it!

Edit: Or did @John Galt get it first? Ordering of posts & the time stamps are not making sense. Congrats to @John Galt as well for calling it.

Probably a dying power supply. It's time to let it go. It had a good life. Drop it off at your local Apple Store for recycling.

+1 it is time to recycle it using one of Apple's free recycling programs. Please click the link below and follow the instructions:

Apple Recycling Programs

Actually it is likely to be a failing Hard Drive. Some Hard Drive failures can sound like a rattling noise. Once the Hard Drive spins up & goes ready, it may allow the computer to boot. My money is on a failed Hard Drive, but you could also have more than one issue.

Looking at it from the front.

The Power Supply is top left.

The Hard Drive is top middle.

The SuperDrive is top right side.

Sadly because the Early 2009 iMac is 16+ years old, it is useless and not worth fixing.

I would think if the issue was the hard drive not spinning up, you'd get an error message indicating a failure to boot. Failed hard drive doesn't seem to fit with the symptoms as outlined in my experience.

"after a long time of being plugged in (which seem to get longer each time) the electric noise stops and then I am able to power on the device"

here's a new one for me: just installed an OEM Samsung sspolaris (2019) 500GB SSD in a 2019 iMac i7 -- and it turned the iMac dead (no power when pressing power button)

when I removed the SSD the iMac powered on (no SSD in the machine)

backstory:

I upgraded the original fusion SSD with a WD BLACK it worked great for a month, but started getting sleep issues every few days (3rd party PCIe controller)

I just bought a 2TB and 500GB sspolaris SSDs to go back to factory SSD on two iMacs

I removed the WD and installed the 2TB Apple SSD and it tested good in the 2019 iMac

next I removed the 2TB and installed the 500GB to seal it back up, but it wouldn't power

my bet was on the SSD (before trying another power supply or swapping cases) -- and it proved correct...