I found on aliexpress

bcm43362kub6

Wii u not opening any games, apps and even system settings (stuck at load screen on any case).

Fix: This may caused by a faulty bluetooth adapter (Test if you can sync a wii remote or pro controller to make sure). Change it and everything will work again.

Gamepad not turning on can happen too if it have a faulty wireless module (2878D-MICA2). You can test it easily using a charger.

If it blinks an orange led when charging = dead battery. If an orange led keeps on even when you disconnect the charger = faulty wireless module.