Why does my iMac A1312 EMC 2429 not turn on after long dormancy?

One drastic but effective solution might be to reinstall macOS. It addresses deeply embedded software issues. Create a recovery drive and reinstall the OS. This can seem extreme but fixed my dormancy issue when nothing else worked.

Software conflicts can also be a culprit. Booting in Safe Mode might help. Here’s how: 1. Shut down the iMac; 2. Press the power button; 3. Hold down the Shift key immediately; 4. Release the Shift key when the Apple logo appears. Safe Mode restrains certain software and can fix many startup problems.

Resetting the PMU (Power Management Unit) might solve your problem. You can do this by: 1. Unplugging the power cord; 2. Waiting for 15 seconds; 3. Plugging the power cord back in; 4. Waiting another 5 seconds; 5. Pressing the power button. This approach has helped me with several Macs over the years.

Your iMac A1312 EMC 2429 may be experiencing power management conflicts when left in dormancy for too long. The Energy Saver settings might need adjustment. You could try this by navigating to System Preferences -> Energy Saver, and making tweaks to the sleep settings. Another potential solution is to reset the System Management Controller (SMC), which helps manage power-related functions on Macs.

Sometimes, the problem is caused by external devices. Try unplugging all peripherals: USBs, external drives, and even the power cable. Let the iMac rest for a while. I had a USB hub causing startup issues, and disconnecting it did the trick.

I’ve dealt with this issue myself, and in my case, the PRAM battery needed replacing. The PRAM battery ensures basic configuration data remains intact, and if it loses charge, you could have startup issues. Replacing the PRAM battery might require opening up the iMac, and if you’re unsure about doing it on your own, a technician could do it for you.

I’ve had experiences with faulty power adapters causing similar problems. Even if the adapter seems functional, subtle issues can prevent the iMac from turning on after dormancy. Using a brand new, official Apple power adapter might resolve your issue.

Firmware issues can also be the root cause here. Corrupted or outdated firmware might not reboot properly after a long period of dormancy. I recommend downloading the latest firmware from Apple’s website and flashing it onto your iMac. You’ll need access to a bootable USB with the firmware installer.

This issue could sometimes be a simple software glitch. You might want to reset the NVRAM to fix it. Try these steps: 1. Shut down the iMac; 2. Turn it on while holding Option + Command + P + R; 3. Maintain the keys for roughly 20 seconds. The system might restart during this process. This reset worked for me when my Mac had similar problems.

In some cases, internal dust could be disrupting your iMac’s functioning. The vents might get clogged, leading to overheating, which consequently affects startups. I recommend opening up the machine cautiously and cleaning the dust using the right tools. Make sure to unplug the iMac before doing this.