It's strange because for many weeks the network was connected & thus, I was able to use youtube, amazon, & other apps; now I can't ??
Most Vizio's have wifi as well as ethernet connections.. So which one you use determines what has to be done to setup the TV.
IF it is by wifi, go into settings, go the network settings, select the proper SSID and Password and connect. Sometimes even once setup you may need to "refresh" the connection. In some cases REBOOTING the router will cause a refresh, other times you may need to do that from the TV. (To reboot, unplug power, wait 20 – 30 seconds reconnect power to your router) To refresh from the TV "test" the connection.
If using ethernet connected direct to your router (best method) and your TV shows you do not have a network connection… you will need to reboot the router and the TV.
Router first, TV once router is rebooted!
Reboot the router. Check the connections.