Galaxy s4 issues

[masterkickass7]

My dad has a galaxy s4 sometimes when he gets a call he and he swipes to answer it and it goes to a black screen he then needs to restart It and it starting to do it more often any ideas he's running Android 5.01

[Black Ops]

U could try doing a factory reset to see if that resolves the issue. Tell him to don't install any apps so you can identify if is an app that is causing the issue