no ringtone on incoming calls iPhone 4s

Do you have Do Not Disturb turned on? Settings>Do Not Disturb. Do you have the mute switch engaged? It's the little slider above the volume buttons. Sometimes cases that don't fit quite right will push against it, too.

Have you checked your volume? Have you checked to make sure you have a ring tone select that actually makes a sound. I have one that's just silence I use for certain purposes. If that accidentally got set as a ringtone on my phone, it would be rather confusing.