Since I updated to Lollipop 5.0 my mobile data does not seem to work. It works when I am checking for system update but not for anything else. At the moment it is either use wi-fi or nothing. This is after update, cache clear and factory default reset. Hopefully a patch fix will be out real soon.
Turn off the phone, then remove the battery and SIM card. Re-insert the SIM, the battery, and then turn the phone back on. It should refresh the network connection.
Also, check the settings to be sure the Network mode is LTE/CDMA. It may have been set to Global after the update, and that tends to cause issues.