Remove the power to your router. Wait a couple of minutes and then power it back up again. (Yes, I know that you're probably getting wi-fi to your laptop, mobile phone, printer or whatever, making it seem extremely unlikely that the problem is with your router but it's amazing how often power cycling a router can still fix connection problems!).
If that doesn't help, reboot the Firestick ;
Turn off the TV and remove the HDMI stick from the HDMI Port.
Disconnect the Fire Stick from its power source, and wait for a few minutes ;
Turn on your TV ;
Reconnect the Fire Stick ;
Press a random button on the Fire Stick remote and keep it pressed for a few seconds before seeing if things are back to normal.