Thanks for your responses but solution was not as drastic as some feared. I remembered after posting that this happened after some Windows updates were installed. So, knowing the install date of the 24 or so updates I worked through them removing them one at a time and checking - a laborious process - until I found the culprit. This was update KB2875783. As soon as it was gone all was back to normal!
I have re-installed all the other updates but that one gets a wide berth from me!
This isn't the first time that a Windows 7 update has messed up something on my system. MS are getting careless, although to be fair with so many different systems running Windows things like this are bound to happen.
At least me and my FO are on speaking terms again! :lol: