I contacted Nintendo, and after unplugging it for 15 seconds didn't work, I shipped my Wii U back to Nintendo.
7 days later, my Wii U has arrived in the mail. It's a brand-new unit. The day-1 update was preinstalled. When it came time for my NNID, it asked for my old NNID, my NNID password, and my email address. It warned that if I continued I would no longer be able to use my NNID with other Wii U consoles. I hit ok and it sent my to the Mii maker. New console, old NNID. It had notices I had accrued while my Wii U was away.
Only negative is that my Nintendo Land disc was stuck in my Wii U and they did not return that to me. I told them it was in there, both on the phone and in the letter I was told to put in the package. Guess I'll have to call them tomorrow.
Still can't access the eShop. Might have to send the console in for repair AGAIN. This is getting ridiculous.
I just received my Wii U today after sending it into Nintendo to get repaired. I was able to open my eShop once, but then it wouldn't let me. It keeps giving me the error code 107-3133, which Nintendo support doesn't recognize. Everything else works fine. Netflix, Miiverse, Internet browser, all that stuff. It's just the eShop that isn't working. Anyone else having this problem? Anyone else fix it?
I'm getting the same error they're getting. I haven't called Nintendo yet. So frustrating.
Yeah so here's what I found out with mine: if I created a new Nintendo Network ID it would let me login to the eShop one time but only once before it gave me that error code. I can create as many NNIDs as I want with the same result. I can get in once but if I leave and then immediately enter in again, it gives me that same code. I worked on the phone with Nintendo for 4 hours without a solution. We changed tons of settings in my system, I tried using a different modem and wireless router, etc. But we never found a solution. I had to send it in again. As of yesterday, they said they had no reported problems with other systems. In fact, they didn't even know of the error code before I called.
So unfortunately, it's very likely you'll have to send your system in again as well. Sorry for the bad news...
Update 2: Looks like the system maintenance cleared up whatever problem was causing repaired Wii Us to be unable to connect to the eShop. I wonder if that was the reason for the maintenance in the first place.
Anyway, I am currently "redownloading" NSMBU; so yes, you can do that.