I tried rooting my Samsung S4 Active and it has gone to home screen. I inserted my sim and I get no service. Someone advised me to check the imei# of the phone and when I dialed *#06# on my phone, it said "null/null" which I'm assuming is zero. I tried hard resetting my phone but you cant since it takes you to ROM loader for some reason. I really have no idea what to do, can someone help me please. 
