Device won't turn on and doesn't appear in 'Devices and drives'

I've had the Garmin Edge 25 for about a year and a half now with no problems at all until the last few months. It started off not turning on at first attempt, and then as the weeks went by it sometimes would take several attempts to turn on. Its current state is that it won't power on at all, and 2 separate laptops won't recognise that a device has been plugged in at all. I've tried the 2 different ways to master reset it (LAP and START/STOP with POWER button, POWER button with DOWN arrow) but neither of these ways have worked.

Any suggestions?