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It might perhaps be that the Garmin device is stuck in time-set mode. So to eliminate that as a possible cause, I would advise that you try to set the time on it, and see if it responds to that. (If it doesn't seem to respond at first, try going through all the button-presses that would set time on it, in sequence, and maybe it will 'pick up' on the sequence at some point and start working again.)
But I doubt that. It sounds as if it has a severe internal control circuitry problem.
If so... How old is it? and, would you consider removing its battery and letting it have a 'rest-reset' for several days? that might bring it back to life again.
I'm glad to hear that.
How old is the watch (or its battery, if the battery is not the one that came with it originally) ?