Do you know, you've done it again! Magic! I'd gone into Folder Options -->File types etc, but couldn't delete the offending entries. Now I've followed your instructions for the registry and deleted Open and Explore. While they are still there in the right click menu, with Explore in bold, this menu looks exactly like the one on this computer and it is all now WORKING!

My drives once again open from the Explorer window as I want them to. What's more (different thread) they have the proper drive icons. Many thanks, this was incredibly useful and I'm going to save that registry key address in case of future problems. I'm so pleased to have sorted this annoyance out and very grateful for your help