That happend to my watch yesterday.
I was about to go for a run, so I declined the update ("Remind med later") - and during the run, the distance didn't show and the back button didn't work.
Then it completely stopped when I ended the workout - screen froze on "saving".
So I did a fored restart (pushing the off button for 15seconds) since charging didn't help either.
The restart helped - everything works - although now the only language option available is english, so something is still not right yet.
If you cannot get it sorted out, contact customer service directly at Garmin, I got help there last time.
I have this issue too have only had my 735XT about a month. Back button doesn't respond, but now seems to activate repeatedly without pressing. Watch is virtually unusable after only a few weeks. Will be seeking a refund.
+1 for this issue with my watch as well. Exact same issue. Did anyone figure out how to get this fixed? What a waste for such an expensive watch to break like this.
Same thing here, only with The up/ down button: keeps on scrolling down And the up button does not work.
After last update (Should be coincidence)
I just did and I was really disappointed by their after-sales support. Although the watch is still under warranty, they told be that I will have to wait 1-1.5 month for replacement and pay also for the costs for the watch to be shipped to Europe's central service. I really want to escalate this somehow!
This has happened to my watch today. Gutted to read the above thread, because it seems that my watch is buggered. I've just been raving about how much I love it and all of I sudden I went over to it and its not working.
I'll be chasing Garmin up myself. Did you just contact them directly?
This happened to me too: gamin stuck on 'clear user data', back button not working and all I could do with it was turn it off and on.
I fixed it by first installing all new updates, which took 2 rounds of connecting & disconnecting it to Garmin on my laptop.
I then had to do the 'hard reset' steps 3 times in a row before it came back to life and is functioning properly now.