Have you tried this:

https://support.garmin.com/...73d0-000000000000%7D

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"Unless you have a ... GF who might put out that night and that night only ... skip it and race." - AndyPants 3-15-2007

Hold the power button down until it shuts off. Might be 20-30 seconds or more. Just be patient.

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Peaks Coaching Group Elite Coach
CVR Athlete Recruiter/Women’s Race Development
USAT/USAC/USAS/USATF Certified Coach, ACE CPT/Sports & Fitness Nutrition/Youth Fitness Specialist

Unfortunately, neither of the two suggestions offered above got it working again, but I got the following advice from Garmin Tech Support, and the watch now appears to be responsive. I'm posting what tech support sent, in hopes of helping someone who finds this using the Search function, when their 910 craps out unexpectedly. One thing I think helped was totally draining the battery before trying any of these. Counter-intuitive, but it worked. .

I'm not sure which of these got it working, as I tried all of them:

Please try this reset step off the charger first.
--To do a soft reset, press and hold the Mode + Lap/Reset buttons for 10 seconds.
You will not see any message while doing this.

Now you should be able to power on the unit like normal.

If it requires you to do this every time you try to power on you will need to do a soft reset, followed by a master reset.

This will erase all user data.

With the unit off the power supply press and hold Mode + Lap/Reset for 3 seconds.
Let go and press and hold Mode + Power until the message comes up asking if you want to erase all user data.

Select yes and then place the unit back on the charger.


--If that does not work please try holding the power + enter buttons for 20 seconds.

--The last thing is to plug it into the charger please then hold down the down + enter button for 10 seconds. If none of these reset work please let me know.

Mine did the same thing today and the advice below worked perfectly.