@zaicopx

At your post isn't visible WHY you need to attach the Nuvi device to PC.
To update device SW or to just update maps.
Atleast if you have a working unit - in most cases SW update is not mandatory, but even you haven't a USB connection - it's still possible to use SD card for new maps - just put them via SD card reader at correspondent folders on SD card and put it back in device. Hint - you can use LM status to get updates DIRECTLY from Garmin servers via [Only registered and activated users can see links. ] application - You can find detajled explanation at [Only registered and activated users can see links. ] .
In case you need to update SW - then for sure you can try to check BEFORE to do anything device to PC connection in usual way - like MTP devise and in so called pre-boot mode ( take a look over conversation at [Only registered and activated users can see links. ] ) - if you have it in ANY, but not other - then drivers are bad, but if you do not see it even in MTP or Pre-Boot - then USB port / USB communication is damaged.
If you have USB communication broken - then - SD card operations are ONLY posibles. Yse guide from Neil to restore your device SW. Also you can use this way to manipulate device data - files for updates, maps, ect... but ... have in mind what you do. Probably will be cheaper and faster to store needed data on SD card space...
BR, DebeliaMark, BG