Hi Irene_MG,
welcome to the Apple (user-to-user) Community.
Re: Incoming Facetime doesnt ring?
You. might want to check whether Do Not Disturb is on.
If is highlighted, tap it to turn off Do Not Disturb
(When Do Not Disturb is on, also appears in the status bar.)
If "Do Not Disturb" was not the problem:
You might want to check the Contact app's details of people who call you on FaceTime, to ensure you have a ring-tone selected for their calls. (If you want you can have a different ring-tone for each person so you will know who is calling by the ringtone.)
Eg: On your iPad:
Go to Contacts, tap a person’s name, tap Edit,
then choose a ringtone and text tone.
All the best :-)