Distorted or skewed image on the monitor
Loose or defective cable
You may receive a distorted image when the cable is loose or defective. Disconnect the video cable (usually a DVI, VGA, HDMI cable) going from the back of the computer and verify that no pins are bent, burnt or broken. Once verified re-connect the monitor cable.
Refresh rate issue
If the refresh rate is not properly set the monitor may have a wavy or an appearance that lines are going down or across the monitor slowly or fast. This may also cause a flickering affect.
A distorted image can be caused by magnetic (EMI) or other interference. Verify no speakers, fans, or other magnetic devices are close to the monitor.
If the above possibilities have been checked it is likely that the monitor is bad. To verify if the monitor is bad try connecting the monitor to another computer. You can also help verify a defective monitor by connecting another monitor to your computer.
Note: Connecting your possibly defective monitor to another computer will in no way harm the other computer.