This is what's on the TV screen. Note that the device name is displayed as "Chromecast5500", whereas ever since I originally set it up, it has shown up as "LoungeTV" - this is why I wonder whether the device has "reset" somehow.

When I start the Chromecast app on my phone, this is the first screen I see. I have hidden the SSID of my home network, but you can see that the app is detecting the device as the same Chromecast5500 name shows in the app as on the TV screen, but it says Needs setup. Also note that in the phone's status bar, wifi is on and I'm connected to my home network.

So I select the device in the app and this screen appears. Again, the Chromecast5500 device is found, and again note wifi is on and I'm connected to my network.

So I tap Set Up and this screen appears... and stays on the phone for over a minute. If I look at the Chromecast device during this time, the light is blinking white the whole time. Note that the wifi logo disappears from the phone status bar in this step, as though my phone is disconnecting from my home network and trying to connect directly to the Chromecast.

Until this screen finally appears. I assume the code it's talking about is the Chromecast5500 name - I can't see the image because the dialogue box is covering it, and if I tap OK it returns to the first app screen shown above.

And this is all it does now. Any ideas?