Thanks for the Reply Gfretwell!
I've had it unplugged from the computer, & tested the Monitor independently, i.e.just with the Monitor power supply plugged in.
Press the on button, button LED shows green, screen displays Blue, Red, Green boxes which move around screen for about 6 seconds, screen then goes blank, Green LED still showing in on/off button.
Same results with Monitor connected up to PC.
Have tried similar PC & Monitor both OK.
Monitor out of Warranty as 2/3 yrs old.
All I Wanted Was A Cup Of Tea!!