iMac 5k keeps crashing

[chipboard]

When i leave my iMac on and come back later to it, it won't start with mouse, I have to hold start button to turn off then restart. it then comes on with message, your computer had to restart because of a problem
My iMac is 2014 iMac 5k with 3 years warranty, Last week after it restarted and i went to open an app screen just flickered on and off fairly quickly. I then had to hold start button to turn it off, i have included some screen shots of the crash, can anyone shed any light on this.

 

[keysofanxiety]

The symptoms you've described are synonymous with a faulty GPU.

 

[Cape Dave]

I had similar issues. Was so frustrating. I think I reinstalled the OS from scratch and also changed my poweer settings to https://www.dropbox.com/s/k6uf5tbvjhnwdqe/Screenshot 2015-11-29 19.26.40.png?dl=0 No issues for many months after that. Still no issues. Could still be what he said above, but worth a shot.