What are the specs for this system (make/model of all installed components)?
What make model of PSU? Do you have access to another GPU?
The PSU should be adequate. The GPU could be defective (I suspect this is the issue).
I assume you aren't trying to overclock anything (CPU, GPU, memory). If so, revert to stock speeds.
You have those issues on safe mode? Do you have another monitor to test? Enven a tv? If rhe error doesnt occur in safe mode maybe you have a driver issue. Try DDU and reinstall your drivers