Can't have G,E,3G,H+ in the network bar (thus no internet connection unless on wifi)
There are many things that can go wrong when messing around with the network settings, but the main ones to check are: 


that you have enabled Packet Data and is not Roaming on
different network
and that you have not set and exceeded your data limit. This can be
    both from your provider and also as a user defined setting.