I had the exact same problem with a Vista cx ,Garmin sent me as a replacement..after trying everything you normally would,including a cold reset and update i sent it back to Garmin who replaced it with a Vista hcx...problem cured.
I can only heap praise on Garmin....I sent my Vista C in for the usual problems,loose rubber/switching off.48 hours later get a Vista cx in return...however it wasnt very accurate and after doing various things Garmin suggested i sent it back......24 hours later i get a nice shiny Vista hcx !!!!!!!!!!!!!!!!!!!
Hats off to Garmin...Superb service
Just sent my third Vista C back to Garmin for Repair/Replacement...faults..rubber peeling off..keeps switching off when it feels like it...lets see if the Superb service persists.