Why does by screen have strange patterns and start rebooting?

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Computer has been working fine and is only used to remote access another computer using Splashtop. Today it started making some strange purple patterns and then rebooting. I really want to keep this old girl going.

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It Seems Like a GPU Failure.

The Pieces may not be compatible or the GPU may be damaged, try Properly Shutting Down the PC or If it does not work you may need to buy a new GPU, Also Make Sure the Current GPU is attached properly.

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Lets see if you can get the system to boot up in Safe mode, Restart your system and press the Shift (⇧) key on your wired keyboard.

Reference: Mac startup key combinations

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@NIM0 HQ - Lets work on better diagnostics before jumping! iMac's are not like Windows PC's they have their unique issues.

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@NIM0 HQ Thanks. I waited a day and rebooted. It looked to be fine and then started doing some slow horizontal refreshing on screen. I then restarted again and it was working fine. I got Macs Fan Control to see how temperature might be impacting. Seems that the GPU is reaching 71 degrees C whereas other components <50 degrees C. Got me thinking that maybe the cooling fans are dirty and I should open it up and clean.

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@danj Thank you. it wasn't allowing me to do so yesterday. Trying to see if any clues in the boot logs.

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