O.K.first of all, many thanks for your replies, but I think I may have used the wrong wording in my initial question.

When I said my Nuvi 200 no longer worked, I meant it is no longer capable of directing me to turn left or right or whatever. My unit works, in your terminology, in so far as it switches on and powers up, but it only gets so far, until it displays a screen saying "No detailed maps found that support routing. The nuvi cannot be used without them."

I can't remember which file(s) I deleted, it happened a number of months ago.