This situation can occur if you 'ask' the monitor to
operate at a higher resolution than it was designed to do.
If after changing the resolution for the monitor display settings in the
'Display Properties' box, the image is 'scrambled' as a result, then:
Re start the computer and press the F8 (function) key
during load at a point when the machine is beginning to load 'Windows
A menu is presented - choose 'Safe Mode'.
Wait whist the system chugs through a safe loading procedure.
When the 'desktop' is presented go to 'Active Desktop' (by right clicking
the 'mouse' in the desktop area)
Or go via 'Start' >'Settings' > 'Control Panel' > 'Display'
In the 'Display Properties' box click on 'Settings', then choose the appropriate
resolution setting for the monitor.
Shut down and re boot system, all should then be OK.