Q: My iphone 5 would stop with FaceTime sign in pop up every 5 seconds. Anyone have an answer?

Greetings Rong66,

Welcome to the Apple Support Communities!

I understand that you are repeatedly prompted to sign into FaceTime on your iPhone. In this situation, I would recommend signing out of your Apple ID for FaceTime and then signing back in to re-activate the service. The attached article below describes how to sign out of FaceTime. 

Sign in with a different Apple ID on your iPhone, iPad, or iPod touch - Apple Support

FaceTime

 

1. Tap Settings > FaceTime.
2. Tap your Apple ID, then tap Sign Out.
   
3. Tap Use your Apple ID for FaceTime.
4. Enter your Apple ID and password, then tap Sign In.

Cheers,

Joe