The last few days whenever I've started up my Wii U the gamepad's been acting as if the console isn't there. It gives me a message that the console is out of range or missing or whatever, then says to restart the gamepad. I do so, and the same thing occurs.
As this is happening, the console is not outputting any image to the television. The only way to turn it off is to hold the power button down. After turning both the console and gamepad off, turning them both back on results in everything working normally, aside from the warning about having forcefully powered down the Wii U.
All of the above occurs no matter how I turn the console on (Power button on console, power button on gamepad, swapping discs). The only changes that have occurred in the last few days are I've obtained a few new games: Super Smash Bros. for Wii U, LEGO City Undercover, Shantae and the Pirate's Curse and DuckTales Remastered.
The only relevant help topic I've managed to find suggests resyncing the gamepad to the console but I can't do that if the console's not outputting video.
The console is hooked up via HDMI, if that matters.