What should I do if the HP Z420 Workstation monitor display is blank during operation?

Try plugging the monitor into a different video port on the computer if one is available, or replace the monitor with one you know is working. Also verify that both the computer and monitor are plugged into a working electrical outlet, that the monitor is powered on with its green light showing, and that brightness and contrast controls are turned up if the display appears dim. (Page 46)