Why is my Galaxy S3 4G losing it's connection and switching off?

A

AC Question

Hey,

Recently I have had a problems with my phone. Whenever I'm using internet with my phone and browsing online, it usually loses it's connection to network. Then it logs me out from the phone so that I have to sometimes insert PIN-code and then password, and sometimes just password.

At the same time the screen might get brighter and it has kind of a waves flashing across it. And sometimes after getting that the phone reboots completely.

Thank you for your help!