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I had that on a 510. Switched it on, did a bit of a ride then paused it. It shut itself down after a few mins of being paused and wouldn't come back on. Got home to find it had completely reset itself to factory (beeps switched back on etc) and had lost the ride. It's been ok since then, but had a couple of times where it's stuck on the initial Garmin screen and rebooting won't work. Plugging it into a charger got it out of that, but it already had mostly full battery.
Does it still have battery left when you get home to try the reset? (Sounds stupid I know, but there seems to have been a semi-common problem with the battery draining itself entirely whilst in 'standby' mode - with people not realising until the screen goes black next time they try to use it)