As a result of messing about as root I now have a blank desktop for this
user. I think the last thing I did was try to browse the contents of a
Win2000-based computer on my home LAN. After this I switched to an
unprivileged user to try the same thing, saving my settings as I logged out
of root..

I can't see anything on the usual forums or in Google which describes this
condition. What is the most likely mistake I have made?

How do I reset my root desktop back to its default state? (There's nothing
of value in terms of user data under Linux yet,, so if necessary I will
re-install from start).