As far as I could understand, Tomtom had (or decided) to change the file system in the latest devices, as with the FAT/FAT32 they were infringing Microsoft claims.
So, at low level, the drive should be Linux based (ext2/ext3/ext4).
I would suggest to try with this:
[Only registered and activated users can see links. ]
and check if the driver gets visible.
Another try: Choose Start–>Control Panel to open Control Panel. Click Computer Management to open the Computer Management window.
In the Computer Management pane, expand Storage, and then click Disk Management.
Check if the driver is visible from here (maybe as a hidden one).