Jim has a Chromecast for streaming to TV via Wi-Fi. Leo says that's a great device. Jim says that the Chromecast button that's supposed to appear in all media apps has disappeared, though. Leo advises relaunching the Chromecast app and also make sure the Chromecast is seated in the HDMI port properly.
If the light is blinking, then it's not online, so it could be having trouble connecting. Jim should unplug and plug it back in. That's how Google updates the Chromecast and maybe it just needed an update. When in doubt, reboot!