catymag
Thank you, you're the best, I appreciate your help.
Will follow your instructions and run chkdsk first without the /r switch, then if need be I'll run again with the switch.

Forgot to mention in the original post the Nuvi 670 works properly in all functions and passes all the diagnostics checks.
I'm just pissed to loose 829 MB of valuable memory.
I'll post what the results were, and if it corrected the problem.