My Wii U also freezes at the Wii U menu screen after 5.0 and an HDD connected.
I finish Mario Kart 8, Close and go back to the Wii U Menu, but it gets stuck on the white screen with the Wii U logo and Wii U Menu text right below it, both on my TV and gamepad. I do have a Western Digital External HD (250 GB) connected. It happened last night and just now again.
What's going on, Nintendo?