HP EliteOne 800 G1 Maintenance & Service Manual page 150

The picture is broken up, rolls, jitters, or flashes.
Cause
The monitor connections may be incomplete or the monitor
may be incorrectly adjusted.
Monitor needs to be degaussed.
Image is not centered.
Cause
Position may need adjustment.
"No Connection, Check Signal Cable" displays on screen.
Cause
Monitor video cable is disconnected.
140 Chapter 8 Troubleshooting without diagnostics
Solution
1. Be sure the monitor cable is securely connected to the
computer.
2. In a two-monitor system or if another monitor is in close
proximity, be sure the monitors are not interfering with
each other's electromagnetic field by moving them apart.
3.
Fluorescent lights or fans may be too close to the
monitor.
Degauss the monitor. Refer to the documentation that came
with the monitor for instructions.
Solution
Press the monitor's Menu button to access the OSD menu.
Select ImageControl/ Horizontal Position or Vertical
Position to adjust the horizontal or vertical position of the
image.
Solution
Connect the video cable between the monitor and computer.
CAUTION:
Ensure that the computer power is off while
connecting the video cable.