When a Wii U is stuck on the White Screen with the Wii U logo, there are a few ways to try to fix it.[br]
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The first is to move your Wii U Gamepad reaaaaaally far away from the console, and then power it on when you are sure it wont be able to connect, and see if it starts.[br]
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The second is to power off the Wii U and bring your Wii U Gamepad back into range, so you can use your Wii U GamePad, Wii Remote, or Wii U Pro Controller, to power on the Wii U again.[br]
Press/Hold B when the White Screen with the Wii U logo shows up, it may load into vWii mode, and from there you can exit to the Wii U Menu.[br]
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The final option is the most difficult, make a hardware dump of the current state of your eMMC user data, and Wii U NAND.[br]
And try to manually repair the dumps on a PC.[br]
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Here are some images from WiiUBrew, good luck![br]
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eMMC:[br]
[image|2630536]
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NAND:[br]
[image|2630538]