Does your CPU has integrated graphics? You can remove your GPU and then you test if the error still occurs to find out if your GPU has damage. You can also test a live system, to exclude issues in your OS or driver configuration

Which OS and GPU do you have in use?

You can run Memtest, just boot it and check the ram. Some Linux distros have memtest included in their bootable image (e.g. Ubuntu). Otherwise you can create a bootable stick with memtest by yourself.