Random Shut Downs!

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Your Mac's Specs
Mid 2010 iMac 21.5"
About a week and a half ago, my wife noticed that the fan to our iMac was running a lot more than normal. (mid 2010 21.5") At first it wasn't a big deal but then it began shutting itself off during the fan mayhem. We thought it was overheating, there is nothing within a 4' perimeter of the iMac minus the back wall which is about 1.5' from the back of the iMac. It is next to a large window but with it being 10 degrees outside I don't think this is an issue, plus we can literally feel the cold off the window. Still, daily the fan would "sputter" for a few minutes then run constantly, then just shut down in use. When we would reboot, it would work for the day then do it again the next day. We tried shutting the computer down more than normal to give it a "break" but that had no affect. We noticed overall lag in the computer, so we upgraded from 4GB ram to 20GB ram two days ago. Since then we've gotten shut downs x3-x4 times daily. The overall "lag" before is gone, as expected, but it does no good if the computer won't stay on. It still gets random fan spasms, then the fan runs high for a few minutes, then shuts off. Upon start up, it will go to a white screen with a cursor, then shut off. Upon all start ups, it tells us it was randomly shut down and will take a few minutes to reboot. Normally I'd blame it on the ram upgrade, but it started before that. It also has more ventilation now than it ever has, including a colder draft from the window. I've read multiple forums on how to "fix" this but none have really worked. I've tried plugging it in a new outlet, took it off the power strip, unplugged everything from the power strip, moved it to different rooms, ect. Any ideas? If you need any information, I will do my best to get it to you quickly!
 
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Your Mac's Specs
Mid 2010 iMac 21.5"
So I restarted it in Safe Mode a few minutes ago. It loaded up to the login screen and for a few seconds the screen did a sequenced flashing like the wave from about the half way point up. I logged in and everything looked to be okay. I opened m browser (Chrome) and the sequenced flashing started up again. So I decided to shut it down completely, wait a few and power up. When it started up, it said that I had shut down the computed due to a problem, brought up the icon and load bar, then about an eighth of the way into the load bar, it stops moving and starts beeping loudly at me. Three loud beeps then a short pause, it sounded like the self destruction sirens on movies. So I held the power button to shut it down again after a few minutes of hearing the beeping over and over. Again I loaded it back up, the load bar went to about the quarter mark then to an all white screen with cursor. At that point it brought up a window that the computer has been shut down due to a problem and would I like to open my pages that were up. I had to wait 60 seconds, open button and a cancel button. I waited the 60 and currently not having any issues for now. Any ideas?
 

chscag

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Your Mac's Specs
2017 27" iMac, 10.5" iPad Pro, iPhone 8, iPhone 11, iPhone 12 Mini, Numerous iPods, Monterey
First of all, you need to understand how your 21.5" iMac cools itself. You'll notice there are vents at the top of the display and at the bottom left and right of the memory panel. Cool air is drawn in from the bottom and warm air exhausted from the top. Plus your iMac has three fans: CPU, Optical Drive, and Hard Drive. Very likely the fan you're hearing is the CPU fan as that is what cools the CPU and surrounding heat sink.

The loud beeping, 3 beeps, indicates that there is a problem with the memory. You might want to open the memory door and re-seat the new memory you put in. It's also possible one of the modules is failing or intermittent.

The original problem with the fan may be due to overheating or dirt inside of your iMac is clogging the air flow of the CPU fan. Why don't you download a free temperature monitoring app or you can buy one that's inexpensive from the Mac App store, and install it. That will allow you to keep an eye on the temps and how fast the fans are spinning.

iStat Pro for Mac is free and will show temps and fan speeds
 

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