I found this: Quote: "Built-in self test (BIST) can be run only when the video cable(s) is unplugged and the Dell monitor is in self-test mode.". More information and other instructions here: https://www.dell.com/support/article/en-us/sln128867/how-to-run-diagnostic-test-on-a-dell-monitor?lang=en#BISTJim.