Just purchased the Droid Turbo on Black Friday. Yep, you guessed it, I soon discovered my phone won't ring. I went into clear the cache partition and it's ringing (go to Motorola site and search for clear cache partition for step by step process). Unlike others, I'm not flipping out, I just fixed it myself. Will see how long this works, I have 14 days to return it if it stops again.
TRY THIS: Hit the Volume up button, notice that under the volume bar there are three icons. One is to allow no interruptions, one for priority only, and the last one allows all notifications. The one for priority is most likely highlighted, tap the "All" button, and now it should always work.