Sleeping M4 iMac shuts down and hard to reboot

It seems my severe issues may be related to my Time Machine backup. I disconnected the drive before a restart. My computer seems to be working. I tried plugging the Time Machine hard drive and I got beachballed within a minute. Since installing Tahoe Time Machine backups were taking days, and wouldn’t complete. I can make a different backup, I suppose, but I have files on a partition I’d prefer to keep.

I turned Time Machine off completely in Settings. It’s not enough to set to backup manually.

Time Machine was on half of a 5TB HHD that wouldn’t fully mount. The other partition had some things I’d rather keep.

I booted in Recovery mode. Disk Utility opened there, but not when using the computer.

I erased the Time Machine partition. I think it took a few tries.

I restarted. The disks wouldn’t fully mount. I got the do not eject message when I unplugged. So it was sort of half mounted.

I used WD Utilities to mount. It actually worked. I can get in to Partition #2, and copy out any files I want to keep.

I believe the issue is indexing. That’s why Time Machine was as if I’d never backed up. It was indexing from scratch.

I believe it was indexing every Time Machine backup I’ve ever done, on a slow drive, with 5 TB of storage. Of course Time Machine was taking forever. The drive hadn’t been indexed yet.

Indexing is going to slow things down. No getting around it. But not that slow. My computer was unusable.

I went into Settings, Spotlight, and Search Privacy to prevent Spotlight from searching my other SSD drives.

I couldn’t exclude the Passport partitions because they wouldn’t mount. But now they have. I don’t want to touch anything until I move the folders I want.

Sooooo, I’m currently moving some files from the HHD. Super slow (10 days for 100GB.

Then it suddenly began working right, and it moved the folder in about an hour.

I apologize for the long post, but it’s taken me 6 days and > 100 restarts to get it going.

I hope this helps someone.

Cheers, Jim

EtreCheckPro is an excellent tool for finding and sorting out various problems.

Download and run the free version of EtreCheckPro, from > https://etrecheck.com/en/index.html

Then post back here with your Report, as per > How to use the Add Text Feature When Post… - Apple Community

(Note that I suspect you mean macOS 26.0.1, that's the current stable release.)

Haven't seen this, but since I have a MacBook Pro a power interruption would not have that sort of effect. Two occasions over what time period? If it's a very intermittent issue, those are often tough to diagnose.

Difficulty booting up can result from problems with the file structure of your internal storage. Would be worth running Disk First Aid to check that.

How to repair a Mac storage device with Disk Utility - Apple Support

As a test:

Turn on "Prevent automatic sleep when the display is off" in the Energy Saver settings.

Then select Sleep from the Apple dropdown menu at the end of each day.

It sounds like Time Machine and/or the external hard drive have failed.

Which is why it is a bad idea to use the same external hard drive for Time Machine and File storage.

Try turning Time Machine off and then reconnect the external hard drive.

If it connects without beach balling, see if you can copy the stored files to a different drive.

If it connects and beach balls, then there is something wrong with the external drive and it needs to be replaced.

I have tried everything I could think of. I was able to open Disk Utility in Recovery mode (Disk Utility not working normally) and erased the Time Machine backup partition. Now I can open the other partition and move the files onto my computer or an SSD. It’s very slow, but it’s working. There appears to be a problem with Time Machine. Might be related to indexing a large (5TB), slow HHD. Since installing Tahoe my Time Machine backups take forever, as if I’d never backed up before, and it never completes. When I say “forever”, I mean more than a week. Frustrating. But I erased all of my Time Machine backups, and I can mount the other partition.

Use the following Apple Support Article to troubleshoot the problem.

If your Mac doesn't start up all the way - Apple Support

M4 Pro Mac Mini 64 go memory. I kept getting “Finder not responding”. Finally decided to restart. I’m typing this on my phone. I can’t restart my computer. It’s been stuck restarting for half an hour. Never happened before Tahoe.

All your " Eggs "in One Basket and the basket should fail ?

Scrambled Eggs is what usually occurs as implied by my Learned Colleague @ den.thed has mentioned

For future purposes

To truly protect your non replaceable Data

Have a 3-2-1 Rescue Plan in place and always current

3 Backups using 2 methods and 1 off site incase of natural disaster or un-natural disaster.

Each of the above should be done to a Dedicated Single Purposed External Drive 

Below link is intended to augment what TM Backup does 

https://bombich.com

I hope it helped but I’m not sure you’re out of the weeds yet. I think there are a few issues, all related to spotlight, indexing, folders, and finder. It’s a new Spotlight. Everything appears to be reindexing. My Applications folder was indexing for a week. It’s going to slow things down for a while. I have icons disappearing, then reappearing. I still get “Finder (not responding)". Sometimes I can give it time and it'll suddenly spring to life and open windows. I get tired of looking at a beachball for 5 minutes. If I knew how long it was going to work eventually I could take a break. Nothing makes me feel dumber than spending half an hour staring at a spinning ball. My Time Machine was on a 5TB Western Digital HHD. I suspect the size and the slower speed contributed to the problem. Maybe that’s what’s doing it for you. The day before Tahoe was fine. The day after Tahoe was this. I have no problem losing my Time Machine backups (I’ll back up again). I copied and files I wanted to keep. Good luck.