When I try to use ROKU, I get a picture on the screen with the word ROKU. After a few seconds, a note appears with the NO SIGNAL alert and advises me to check the input which I have done. It seems like the ROKU is not sensing my WI-FI. I have not used ROKU nor this TV in about 6 months. Do I need to sign up for a ROKU subscription? Any help would be appreciated. Thank you.
The words "No Signal" are usually produced by your TV rather than the Roku. This probably is not an error related to Wifi. A properly connected and powered Roku will produce an HDMI video signal even if it can't sense Wifi.
The following YouTube video from the official Roku channel may or may not help: