If you've set up your Chromecast already, but can't connect to it, check the following:
Check 1: Make sure the device you're using for casting is on the same Wi-Fi network as the Chromecast. (When using Chromecast you'll be casting from your smartphone, tablet or a computer using the Google Chrome browser).
Check 2: If you have the Google Cast app on your device then turn it off and then on again.
Check 3: Try casting from another device.
Check 4: Try casting from a different site (such as YouTube).
Check 5: Turn your router off and then on again. Also, take a look at the router settings and see if changing the W-iFi channel does the trick. Your neighbour's W-iFi can interfere if their router is broadcasting on the same channel as yours. Objects such as microwaves, cordless phones or thick walls can also interfere with your Wi-Fi.
Check 6: Chromecast 1 (the older version) only works on a 2.4GHz wireless network, whereas Chromecast 2 and above will work on both 2.4 and 5GHz. If your router is capable of broadcasting both, make sure you connect to the 2.4GHz network if yours is the Chromecast 1.