@BogMaster
Go to [Only registered and activated users can see links. ] and post back here the answers to all the 11 questions in the initial post there. Then we can process with a plan. The microSD may well have been corrupted at the same time but it may just not be allocated a drive letter properly in Windows.
(TLDR: The nuvi's not irrecoverable, don't bin it!). Read behind the spoiler below if you want to know a bit about how it's done:
Spoiler:
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