I was having a similar problem. I could turn the set on and within 15 seconds I would loose function control (volume, mute, channel, menu, etc) on both the remote and side panel buttons. After a call to VIZIO tech support, and trying numerous troubleshooting steps, VIZIO indicated that a technician visit was called for. He arrived yesterday to replace the main board. After initial installation the problem appeared to be solved.
When you do a replacement of the main board you have to go through the setup routine again. To save time, while the tech was there, I did not initially do the internet connection. As he was doing his completion paperwork, I went back into the system setup and proceeded to do my wireless connection setup. As soon as I did I lost function capability again.
The Service Tech in the house contacted his tech support at HD Repair in Florida (VIZIO"S repair support folks). HD repair stated that there appeared to be a conflict with my Linksys E4200 router and that I should look for a router software update or try another router. There was nothing else they could do.
Today I called the VIZIO tech support number again. I explained the situation to the young lady and was told that this was a known problem and appeared to be a problem associated with file sharing. According to her the VIZIO TV does not permit file sharing and will lock up when queried by the router. Normally file sharing, on a PC for instance, is controlled on the individual device. Since there is no place on the TV to turn off a file sharing function, and I cannot find anyplace in the E4200 to do this I am at a loss. She did not have an adequate answer. . I don't understand how this can be true or you would never be able to use the "Smart TV" functions.
Bottom line is that I can use my TV as long as I don't connect to the internet via my router. I cannot find anything in the E4200 setup that would allow me to control file sharing for a specific device.
It is also interesting that there appears to no way, in the TV setup, to "Disconnect" a wireless connection once it is setup, short of doing a "Factory Reset" to clear memory. I also tried doing a hard wire connection with the same results, at least this made trouble shooting easier since I regained function control as soon as the Ethernet cable was disconnected..