No video at the system monitor.
Check that the power cord is connected to the monitor and to the wall outlet.
Verify with a volt-ohmmeter that the wall outlet is supplying AC power.
Verify that the video cable connection is secure between the monitor and the video output port.
Use a volt-ohmmeter to perform the continuity test on the video cable.
If the cables and their connections are okay, then troubleshoot the monitor and the graphics card.