Not showing if someone is calling

[AC Question]

My nexus 5 doesnot show any alert if some one is calling me. It just vibrate but with the desktop screen or the screen in which i am working on.
I am not able to attend the calls. Please help

 

[B. Diddy]

Welcome to Android Central! Have you disabled any system apps? Does it work in Safe Mode? https://support.google.com/nexus/answer/2852139?hl=en