Welcome to Justanswer.com, my name is ***** ***** I will do my best to assist you.
How long have you owned the 920xt ?
Also, did it get wet recently or have anything spilled on it?
even with waterproof devices, if it had something with a lot of sugar spilled on it.. T hat can still make the buttons stick.
Also, just b ecause a device is waterproof doesnt mean that the seals dont eventually break down and let water in.
So I ask again, since the last time that button worked and now, has the device been wet, or had anything spilled on it?
Considering those devices still sell for a substantial amount new.. http://amzn.to/1TOU48A
Its probably a good investment to let garmin repair it at about 25% of the cost of buying a new unit.. As most likely whats happened is the button 'fused' shut over the 9 months the device was sitting there.. This usually happens when the waterproof seal breaks even slightly and the device fills with water, and then the contacts inside the buttons rust and fuse together.
You can get the device repaired here at a flat rate of about 115$ http://www8.garmin.com/support/outofwarranty.html
Other then that.. Dismantling the watch and cleaning the contacts for each button with some wd 40 and then greasing them with silicone so they dont rust again may fix the issue. But if the terminals for the button contacts rusted through completely.. It doesnt matter how much you clean them if theres no closed circuit being made.
Repair, is most likely your only option ) other then replacing it outright (
I strive to provide great service, and greatly appreciate a 5 star rating clicked and submitted when you are satisfied.. I always answer follow up questions.Dustin S.Senior Technician and Network Switching Systems Operator / Maintainer.