I've flashed the GPE rom http://forum.xda-developers.com/show....php?t=2557353 and after that my Hangouts won't sign in. Tried several reboots and clearing cache from Google play services.
Gmail and other accounts using Google works fine, it's just Hangouts that's giving me trouble. I've just downloaded Hangouts and Google Play services today so it's the latest versions. I've googled and what I've found is that similar problems for other people get an error message, which I dont' It just says "Not signed in" and nothing happens when clicking on it or the settings button on the S4.
EDIT: Solved - I took a picture and choose to share it with Hangouts. I then got prompted to sign in and now it works!