Apple iMac (Intel) running Monterey 12.1 cannot restart after move from McAfee to Norton

[Devonex22]

I have a one month old Intel iMac (2020 model) which was running like a dream until I followed BT's advice to replace McAfee with Norton for virus protection.  It used to power up effortlessly in under 15 seconds.  Now it can't power up at all.  The progress bar gets stuck halfway and then it tries to restart over and over again without success, putting up a multi-lingual screen saying it has a problem.  All I can do now is start it with a 'safe boot' by holding down the shift key which disables all the salient features which make the machine run so smoothly.

I uninstalled the McAfee software first using the official uninstaller supplied with the product.  The first two parts of the Norton installation were fast and smooth and the screen said it was installed successfully.  But the next stage was to activate the new product and so I dutifully pressed the button and that's where it all went to pot.

In safe boot mode, double clicking the Norton icon in the Applications folder loads the application but results in a horizontal 'progress' bar oscillating endlessly back and forth in a blank window.  It shows the legend 'pending' but gets no response.  Similarly, if you hit the uninstall button in the top menu that gets no response either, so it can't be uninstalled.

I have tried all the other usual Apple procedures for this situation, viz. starting with Option-Command-P-R, getting into Recovery mode with Command-R and then using disk utility (no faults found) and reinstall Monterey (which successfully took me from 12.0.1 to 12.1) but none of these solved the start-up problem.  I scoured the Norton site for clues as to how to solve it but with no success.  The machine still will not start in anything other than safe boot mode, which is pretty useless to me, not to say incredibly annoying that my fabulous new machine should be reduced to this thanks to BT's decision to switch from McAfee to Norton and by doing so release mayhem among its users as evidenced by all the threads on this forum.

So come on BT.  You caused it.  You solve it, or do I have to invoice you for all the hours I have spent trying to solve this problem with a likely visit to the Genius Bar in the Apple Store 45 miles away to follow.

If anyone else has this same problem and knows how to solve it I would love to hear from you.  Thanks in anticipation.

[Devonex22 · Accepted solution]

The morning after I posted this note I solved the problem myself.

Fortunately I did have Time Machine backups and my latest one was 9 days old (I don't have them set to automatic).  Whilst still in 'safe boot' mode, I used Migration Assistant (Applications > Utilities > Migration Assistant) and reinstated my System Files from the Time Machine disk, and other files and whatever the top option of the four choices were.  The only one I didn't reinstate was the second one down which was the biggest section of all, the named user data.

The result was that my system data was put back to how it was 9 days ago and the transfer has obviously overwritten and eliminated the corruption introduced by the Norton software which totally mucked up the start-up procedure.  The machine now starts up as fast as it used to - under 15 seconds from the SSD drive - and everything works as fast and as smoothly as it did before.  I now also have McAfee reinstalled and working as before, but Norton hasn't given up yet as it is the first thing that leaps into action begging me to complete the installation previously started.  No chance of that yet as I am still very bruised and battered from this whole fiasco.

I also found that my new installation of Monterey 12.1 survived as did all of the latest versions of my daily work, e.g. spreadsheets etc.

Good luck to anyone else who goes through this.  I hope this response helps you.