After Chkdsk you need to remove .chk files to free up space.
Also try Lolypop idea of formating Nuvi drive.

[Only registered and activated users can see links. ]

Lose The Memory card until you have fixed your nuvi.

Remove all unneeded voices,texts,help,keyboards and eula to free up space.

Hard reset and test after every step,Full Backup before deleting any files.