Issue with Lollipop (Android version 5.0.2) on Moto G: unable to pick calls.
The first thing to check is in 

Settings > Sound &amp; notification > Interruptions

that Calls is switched on to allow dialer to bring up the notification window... Then you should get the popup to answer the phone. Good luck though - if your phone is like mine (a Motorola G 2nd gen) depending on what your doing on the phone at the time of the call the stupid call/reject slider doesn't work... WTF - Phones that can't answer phone calls - FAIL!