What to do about iMac restarts every 10 to 15 minutes after Big Sur installation?

brady50 wrote:

Have a late 2014 iMac 27 inch Retina, 4 GHz Quad-Core Intel Core i7, 16 gig memory, 3 TB fusion and upgraded to Big Sur as soon as it came out and upgraded to 11.4. Worked fine for months. Then in the last couple of weeks started to get the dreaded spinning wheel of death and it kept getting worse until yesterday when it totally froze up. I then used recovery mode to install Yosemite which was the only choice I had to re-install macOS. It worked fine yesterday using Yosemite. No issues other than having to start all over. The other disaster is that my time machine backup external drive is not recognized and even though the drive has over 1 gig of data, my iMac doesn't recognize it. Very sad. So I upgraded last night to Catalina. Now my iMac restarts every ten to fifteen minutes. I have tried to use recovery mode to repair all the discs. The Fusion and SSD discs show they are OK. I cannot run Disk Repair on the time machine external drive because after fifteen minutes is restarts. I tried doing this in Safe Mode and it still restarts after fifteen minutes. It appears by all logic that the fusion drive is the issue. What do you think?

Call Customer Support (800) MY–APPLE (800–692–7753)

or on line https://getsupport.apple.com/

or call AppleCare Support at 1-800-APLCARE (800-275-2273)

Outside the USA—Contact Apple for support and service by phone

See a list of Apple phone numbers around the world.

https://support.apple.com/en-us/HT201232

try resetting it! (did you already try this?… lol idk) But if all the things you did doesn’t work, well you may need to bring it into a apple store or get a new one