Nuvi 255, not recognised by PC/unable to upgrade etc

[Sharpthinker]

Hi
When i switch on my Nuvi 255 all is OK until i connect the charger, then the unit reboots and sits with the black"Computer logo" on the screen then it reboots back onto the "where to?" screen. Sometimes it reboots and just stays on the black "Computer logo" screen.
When i attempt to update firmware the pc cannot find the unit, also when I go to explorer the unit is not listed even though I have changed USB ports.
I have tried a hard boot using the hidden button under the sticker, and updated Webupdater to latest version and still no change.
When i hard boot using the hidden button the unit reboots but all my data is intact, so not a factory reset as i assumed.
Thanks
Clive

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