Chromecast won't work after 18 months

[AC Question]

My Chromecast was working for 18 months without problem now it can't connect to WiFi. The Googlecast says it has to set up (was previously set-up) but while running the app on my android tablet it disconnects the Internet on the tablet and tries without connection. The TV says it is trying to establish a connection before it just gives up and says try again or cancel. TV is connected to Internet. I am sure it wasn't a Googlecast before.