Why is my phone behaving strangely?

[AC Question]

I'm using HTC Desire 816G with Android version 4.4.2.
Sometimes when i get a call the ringtone plays but nothing is displayed on screen but after some time i get the Call screen but i can't accept or reject the call.
another issue is that sometime when i open my call log or contacts it shows a loading screen and it is only fixed if i restart my phone.

 

[RogMoore]

I think you need to perform a Hard Reset in your device, in order to make it virus free.