My very expensive Garmin C320 costing some $785.00 in 2006 has now gone on the blink.
Not completely but it is intermittent, it will work OK for while but it will lock up at any time.
Tried all the resets available but has NOT helped at all.
I now use a Nuvi 40 which I got for free.
But I would still like to have my C320 working again.
I have a Nuvi 310 which does exactly the same thing. It doesn't do it very often, but usually inconveniently. I made the mistake of having the sound off on one trip, nearly went into a Fjord before I realised... It only started doing it after a firmware update.