Hmmm...tried all your suggestions last week but to no avail. I think you may be correct about video card settings. I installed the X-Plane demo and in an effort to improve performance I updated my video drivers (unfortunately I have Intel HD graphics on this machine, not the bst in the world) I believe the problem arose directly after I deleted X-Plane and also tried "rolling back" graphics drivers. Also tried 4 different drivers but no improvement. I am further convinced that it is the video driver causing the problem since my other laptop has an Nvidia 9300 graphics processor and works perfectly. What I'm not sure is whether ASUS have a tweaked version of the graphics driver since none of the four Intel drivers cure the problem. I'm looking for an ASUS specific graphics driver but so far no success.
Again thanks for replying, as a retired software developer of some 30 years experience I'm determined to crack this one somehow. Watch this space.
Regards Richard