I have had a Tom Tom live 850 for about 3 years now.
Great GPS easy to use and great functions but mine froze
totally after 2 years but i got a new one under extended
Warranty.I have the same problems as you from time to time.
Mine has been good for about 6 months now but started
playing up this week.Normally once i update mine it comes good again for
some timent is that i got lifetime maps.Also i find it a pain to update.
It nearly always takes a couple of times to update.Good thing about the
replacement is that i got lifetime map update with the new Gps.

Cheers Miles