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If the same thing happens with external or internal battery power, then I think it's not a matter of the power source causing it, at all.
Why not try updating it with Garmin Express? that often cures these sort of problems.
When dealing with an update for your Garmin device, it is best to simply download, install, and use Garmin Express.
and (if you have a Windows PC) click on the big blue Download button at center bottom of the page. (If you have an Apple, click on the nearby Download for Mac link.) And download Garmin Express' installer to your computer, save it, then double-click upon it to install Garmin Express.
Then start the program, Garmin Express. Then connect your Garmin device. Then use Garmin Express to update your device.
(If this helps with the problem and answers your question, please rate my answer. If there are any further problems, please Reply and let me know, and tell me how old the Garmin device in question is measured from its date of purchase ... and I'll offer further advice. Thanks.)
OK, I see. And I'm sorry to hear it.
If the device is not recognized by the computer, then either
A. it's dead inside, not alive enough to respond... in which case, the question is over, it's broken and needs either servicing or replacement.
B. the USB cable, or the USB port on the computer, is not quite 'alive' to devices connected by or to it/them. In which case, try a different USB port or two, and also a different USB cable if you have a spare. (USB ports on a computer can be genuinely different from each other. They are supposed to be utterly interchangeable, but in practice, they often differ in capability and response. So by all means try two other USB ports, preferably ones physically separated from the one you used before... they tend to run on a different cluster of circuitry when their physical separation on the case of the computer is a long distance.)
If you end up deciding to have the Garmin device repaired, let me know, please. Thanks.