iMac (Late 2015) shuts down; urgent TM backup drive needed

iMac Late 2015: Retina 5k 27”. 3.2GHz Quad Core. Intel Core i5. Memory 16GB. OS: Monterey 12.7.6:

Request recommendations for fast hard drive for urgent 15 months of TM backup. Computer regularly shuts down without warning - between 30 mins and half a day.


Small business:

I need to buy a new iMac but can’t get a TM backup for transfer as computer shuts down after short time - 30mins to half a day. It’s random and the reason I need to buy a new iMac. Won’t reboot until I take the power cord out of the computer and reinsert. Taking it out of the power point doesn’t help.


My 2015 iMac is continually shutting down completely to a black screen (since I came back from Xmas holidays) Sometimes it will stay active for 30 mins, sometimes up to half a day. The more I use it the worse the shutdowns get. As I use it exclusively for my business I am keen to back up and get out. Considering it might shut down after 30 mins or might stay alive for a few hours I need advice on the quickest hard drive suitable for a full TM backup for the period Oct 2024 to now. Most of my work is saved to Dropbox and most of my work is done on apps. Outlook is my main concern as I have a lot of emails stored in Outlook folders.


Further information:

I have had regular back up issues since October 2024 and Time Machine backups stopped working at that time i.e. they would not complete - I bought 2 new drives and neither of them would complete.

I have tried backing up to TM periodically since then and most recently last week. The backups always fail to complete. I am using a 2TB portable WD drive and thought an SSD drive with more space would be a better option particularly as the Time Machine backup is trying to backup from October 2024.

Eager to have some advice. Note: I was on the phone to support for hours last week (call eventually dropped out) mainly due to computer frequently shutting down, eventually every 5 minutes even. If there’s a fix for my computer that would be great but we couldn’t even get a disk utility session/check to work.


iMac 27″, macOS 12.7

Posted on Jan 16, 2026 5:09 PM

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Question marked as Top-ranking reply

Posted on Jan 16, 2026 6:05 PM

If you have another Mac, you can also try Target Disk Mode, it involves a lot less of the OS, and might not shut down.


Transfer files between two Mac computers using target disk mode - Apple Support

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6 replies

Jan 16, 2026 5:47 PM in response to janet278

if you cannot manage a TM backup due to frequent, unpredictable shutdowns, you might be forced to move as many files as possible manually to an external drive before each shutdown. and then do it again over and over with successive files, until all of your data has been moved to an external device.


and I wold recommend a QUALITY external SSD for this, as an HDD will really not like sudden shutdowns without ejecting it. an SSD should handle that situation better.

Jan 16, 2026 6:01 PM in response to janet278

If TM has not successfully backed up in months it's going to take a long time no matter what, and the obvious speed advantage of solid state drives is not particularly applicable to TM due to the processing "overhead" it requires... much more so if it has been weeks since the last one.


I suggest starting that Mac in "Safe Mode" and creating a backup while in that mode. It may or may not shut down as it has been, but it's worth finding out. Time Machine will work as usual in that mode.


Start up your Mac in safe mode - Apple Support

Jan 17, 2026 3:24 PM in response to janet278

If you're thinking about buying a new Mac consider the following: a 10 Core Mac Mini M4 with 16 GB RAM and 1 TB SSD ($1084 US) with a 32" LG 4k monitor ($331 US) from Amazon.com)  is $1415 US which is $541US less than a similarly configured new 24" iMac ($1956 US)  re 07/2025. Keep your keyboard and mouse from your current Mac for use with the Mini. 


I got the above Mini with a 32" LG 4K monitor w/speakers for only $60 US more than the 27" (didn't know the Mini had a speaker).  There are many monitors available in 27" size on up for $100 US to $500 US depending on what features you want.  The monitor prices are before tariffs.


If you plan on video conferencing you'll have to get a camera or use your phone.


Just some food for thought.


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iMac (Late 2015) shuts down; urgent TM backup drive needed

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