When the service is disabled in LG G3 mobile :
This might be mostly because network mode might have been changed in your mobile.
Observations :
1. Service disabled in home screen and no network.
2. Mobile network option in tethering &network -> mobile network is disabled.
3. Doesn't change even if you use different SIMs
Steps to resolve :
1.browse for 2G-3G ON OFF in Playstore.
2.download the app by curvefish
3.install the app
4. Now long press on your home screen and select 2G-3G ONOFF widget
5.In the network mode select "Global" or CDMA for 3G.
6. That's it
just check your network connection. Switch off and on the mobile and check again!