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The Garmin Forerunner is, if it is still within 1 year of its purchase date, still within its warranty period.
I advise you, given all the symptoms, to leave the Forerunner on the charger for at least 6 hours continuously, before trying to turn it On again.
If it still fails to stay On or fails to work basically, after that, then you have a Forerunner that is most likely defective within warranty. And should be turned in to Garmin Repair as such, for free under-warranty repair-servicing.
To do this, go to
and use the File A Claim link to start the process.
For information about Garmin's warranty if you need it, here is the page for that:
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