Be sure Anynet+ (CEC) is enabled on your TV. Also try disconnecting any other device from your TV except the Arc until you are able to set it up correctly.

Have you switched on Anynet+?

Glancing through your TV FAQ/Manual online, it says…

Anynet + (HDMI CEC) is activated in the factory for Samsung Soundbar and Home Cinema System. If your device is other than Samsung Soundbar or Home Cinema System, you need to make sure that the Anynet + (HDMI-CEC) function is activated on your Smart TV. 

• For T/Q, R/Q, N/Q, and M/Q series smart TVs (from 2017)

        Home> Settings> General> External device management> Anynet + (HDMI CEC)

• For K series Smart TV (2016)

        Home> Settings> System> Expert settings> Anynet + (HDMI-CEC)

• For Smart TV up to the J series (2015)

        Menu> System> Anynet + (HDMI-CEC)

Hope that information may assist to get the Arc up and running with your TV.

That did it - thanks guys!