My Wii U I got over the summer connected just fine to my Sony HDTV (KDF-E50A10, not sure what the real name of it is). I didn't even need to change any of the display settings on the TV or Wii U--I just plugged my Wii U HDMI cable into the TV and it worked perfectly.
But in September, I had to change locations and, therefore, TVs. I can't remember the kind of TV it was, as I don't currently have access to it now, but it wasn't an HDTV. I had to use the Wii composite (component? The cable that comes standard with the Wii) cable to attach my Wii U to that TV. I switched the Wii U's TV display settings to non-HDMI. Even though it didn't look good, it still worked, and I could get my Wii U to play on that TV.
Now I'm back to my HDTV. I plugged in everything, including the HDMI cable. I went to Settings on my Wii U Gamepad to change the connection type to HDMI. Then it asks me for the resolution and things stop going smoothly. I tried Automatic and it immediately tells me "Unable to apply setting. Check that your TV and console are properly conncted." I go back and try each individual resolution option and it takes its time, but eventually tells me the same thing. My TV is definitely on, and the HDMI cable is definitely connected, but I always get this message.
I tried messing with my TV's settings, but I can't seem to find a way to alter the resolution, just the display (from 4:3 to 16:9). It also only has one HDMI port from what I can tell. This is the same TV that I used without problem only a few months ago, yet now I cannot seem to get anything to work. Any ideas or help are very welcome, thanks!
Update: I tried turning the system and TV off and on again, and unplugging and re-plugging in the HDMI cable. When I turned on the Wii U afterwards, the Wii U opened a notification saying something to the effect of "The Wii U is plugged in using a different cable from before, do you want to automatically change the resolution settings?" I clicked yes, but it still gives me the same error message as before. Again, the Wii U is on, the TV is on, and the HDMI cable is attached to them both.