Well, my Wii U seems to have been bricked. It gets stuck on the white Wii U screen whenever I try to turn it on.
I tried to reboot it to safe mode, by holding down the power button for 5 seconds. Also unplugged the power supply and plugged it back in, after 30 seconds. Neither of these things worked. I called Nintendo, and they suggested I take it to GameStop of all places to get it repaired.
Luckily, I only own two Wii U games. Windwaker HD, and Xenoblade X. I only kept it around so I could play Wii games on it. Still kind of annoyed though, since I'll either have to buy a Wii, or pay to have it repaired.
If anybody knows any other fixes please let me know!