I have the same problem, Tried to disconnect the battery and reconnect it gain, The signal came back and the phone was working normally, I guess this is temporarily, I can't find what causes the No service problem yet.. But anyway try this, Turn off your phone Open it and disconnect the Battery (You may find many tutorials) Then reconnect the battery again.
I had the same problem 2 Hours ago, This is how it was solved, I took out my SIM card and put another one with a different carrier, The signal was working perfectly, Then I put back my SIM card and it was also working perfectly,