Probably a stupid question to ask, but are your computer and console actually connected to the network? I had this problem once before, and it turns out I had misspelled my network password on the Wii U side.
In System Settings, there is a connection test button somewhere. It doesn't matter if it cannot connect to the internet, but if it can connect to the modem, everything is correct on the Wii U side.
Check the same thing on your PC, can you ping your console from your PC?