Yes it does have some hallmarks of a hardware failure and it seems you've already ruled out the USB port connections to the board being the problem. However, there can be other explanations for such behaviour and it's likely to be either (1) another kind of hardware failure such as a bad PCB component or the flash memory is failing; or (2) severe software corruption; or (3) a corrupt file that's required for properly loading during the boot cycle.
- Is likely fatal, in that it's certainly not economically repairable.
- Is easy to fix by deleting any existing gupdate.gcd from .System folder and directly flashing required fw regions using a media card (see below*).
- Is also easy to fix if preboot mode is available..
Check if you have preboot available. Try all the methods in the following link, however holding the top left screen corner works for most nuvi devices: [Only registered and activated users can see links. ].
If it's 'soft-bricked' it won't have access to Mass Storage Mode so cannot be seen in Windows File Explorer or Disk Management. However in preboot mode it will be listed in Device Manager under "GARMIN Devices". Preboot is useful for recovering bricked devices using cure fw.
If the device is simply bricked by a corrupt file you can follow this guide: [Only registered and activated users can see links. ] However usually such devices don't boot far enough to load anything from a media card so that may not be the case with yours seeing it actually can use the card.
*If you want to rule out a firmware problem and it still reads a card in its current state, you can use the SD kit behind the spoiler below to delete gupdate.gcd (if it's present), dump a copy of the non-volatile memory region 154, and properly reflash the 3 fw regions 14, 127 & 158.
Spoiler: Click
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