I had this same problem with my phone not ringing after an upgrade. I was getting ready to try the "hard reset first" as suggested above, and then I read another thread that talked about how it could be related to outdated or corrupt information in the "cache". I already had a free App installed on my phone called "App Cache Cleaner" (InfoLife), so I ran that to clear the cache files on the phone. I did go into the App's Settings and unchecked "Hide Apps with tiny cache size" just in case (not sure that I had to do that, but I did anyway). It takes a few seconds to build the list of Apps and cache sizes so don't rush it. After running the CLEAR, I rebooted the phone and then it started ringing again! Haven't had any trouble with it since. Didn't lose anything, didn't have to re-load any Apps or Contacts or anything.