Reposting the fixed that worked for me so nobody has to go search!
"Well, as everyone else, I got the dreaded "no ring of death" using the "Smart Profile: Face Down" feature. However, I was able to fix it pretty simply, although I've only done it once due to fear that I won't be successful in another attempt. What I did was really easy.
1. Make sure that the "Smart Profile: Face Down" feature is enabled.
2. Hold the phone face up in your palm.
3. Call yourself from another phone.
4. As the phone is vibrating, DO NOT ANSWER.
5. Still holding the phone, flip the phone face down as it vibrates.
6. Then, flip the phone back over so that it's facing up.
7. End the call from the phone you are calling from.
After I did those steps, I left the phone face up and called myself again, and then it was finally ringing! May have been a fluke, but if it worked for me, it may work for some of you as well. I promptly went back into settings and disabled the Smart Profile: Face Down feature. Hope this helps, good luck to all of you."
Many people including me have had this technique work. It doesn't always work the first time, I had better luck after doing the above steps right after a battery pull. Others have had it work the second, third or tenth time they tried. Its worth doing several times to avoid the time involved in restoring from a factory reset..at least it was for me.