Tried most of the above - to no avail however, FL310 was quite correct when he pointed me to the graphics card. Took some photos of the screens then, armed with digital camera went to get advice from those that know at PC World.
They were most impressed 'cause, from the photos, they quickly diagnosed a blown graphics card!
So, having tried restoring windows (which now gives me an annoying start-up option - how do I get rid of that?) I parted with £70 for a new card <img src="mad.gif" border="0"> <img src="mad.gif" border="0"> and now have a perfect picture with everything working again <img src="tongue.gif" border="0"> <img src="wink.gif" border="0"> <img src="smile.gif" border="0">
Thanks for the replies and seasons felicitations to all!