Hold down the On/Off button on the remote for over five seconds, when the set is on, and let it soft reboot.

if this does not fix it, try a Factory Reset.

if that does not fix it, you could contact Sony, or wait for the next software update, or hardwire the Ethernet (or at least use Powerline adaptors for a wired Ethernet connection).

or return the set whence you bought it, as faulty, and get a replacement.