weird looking screen on my imac High Sierra

[fiery]

iMac (21.5-inch, Mid 2010)

After 10 minutes it freezes and i get diagonal lines/boxes.

 

[chscag]

It sounds like a possible GPU failure or failing. Run hardware diagnostics to see what it comes up with.

 

[fiery]

Do you mean disk utility, first aid?

 

[IWT]

Do you mean disk utility, first aid?

You could try that, but what Admin chscag meant, I believe, is this : How to use Apple Hardware Test on your Mac - Apple Support

Ian

 

[fiery]

Here is a picture...

 

[chscag]

Your iMac is going on 10 years old so a failing GPU is a possibility. The link Ian gave you will show you how to run a hardware test on your iMac. That may or may not tell you for sure but the photo of your screen does look like GPU problems. The GPU is replaceable on your iMac but finding one on eBay may turn out to be expensive. The GPU is on a daughter card on the backside of the logic board. The entire iMac must be disassembled. Go to iFixit: The Free Repair Manual for instructions on how to change it out.

 

[fiery]

Thank you.