iMac in Continuous Shutdown/Restart Loop

[robastewart]

2011 iMac 27". While Mail and Safari open, reading a webpage, the screen suddenly went to a black and white vertically striped display. I waited a few moments to see if anything would happen, then the machine seemed to shutdown. But then it appeared to go into restart on its own. It doesn't fully restart though -- a screen appears with the dark gray apple and progress bar. It runs on this screen for a minute or two, then goes into shutdown and restart modes again.

Nothing new or different has been done to this computer in recent weeks.

Any ideas much appreciated.

 

[Pieterr]

2011 iMac 27". While Mail and Safari open, reading a webpage, the screen suddenly went to a black and white vertically striped display.

https://support.apple.com/en-us/HT203787

 

[redheeler]

2011 iMac 27". While Mail and Safari open, reading a webpage, the screen suddenly went to a black and white vertically striped display. I waited a few moments to see if anything would happen, then the machine seemed to shutdown. But then it appeared to go into restart on its own. It doesn't fully restart though -- a screen appears with the dark gray apple and progress bar. It runs on this screen for a minute or two, then goes into shutdown and restart modes again.

Nothing new or different has been done to this computer in recent weeks.

Any ideas much appreciated.

As the poster above mentioned, a failing GPU is very much a possibility based on the symptom of vertical stripes.

For now, I recommend trying to boot into Safe Mode.