iMac won't wake from sleep, is unresponsive

As a test:

Disable the Screensaver if you are running it before sleep.

Turn On "Prevent automatic sleeping when display is off"

Set "Turn display off when inactive" to 5 or 10 minutes

Leave the iMac On and only allow the display(s) to turn Off

Do not manually Sleep from the Apple Drop Down menu

Shut Down the iMac at night and when away for a day

chefpeon wrote:

My iMac is a 2021 M1 24", running Tahoe 26.2.

This has started happening recently, in November of '25, maybe since the last update, but I'm not certain about that.

Sometimes, but not always, my iMac will not wake up from sleep and is completely unresponsive. Neither the mouse, the keyboard, or even pressing the rear power button will wake it up. I have to disconnect my computer from power then re-power it and start it up again. It used to happen after being asleep for a long while, like overnight. But now it's happening more and more and it happens after it's been asleep for short periods as well.

I ran the disk utility, but other than that, I don't know how go about solving this problem.

You can try to run Apple Diagnostics to determine if there is a hardware issue

Use Apple Diagnostics to test your Mac - Apple Support

If I recall, these iMacs have external power adapter brick. Perhaps your adapter is failing.