I have Tales of Symphonia and Smash, but as far as I know there has never been any foreign hardware attached to my console that wasn't either new or formatted just before.
I also checked both the Wii and Wii U menu and I don't see any homebrew channels, so if there was something installed, it's not showing up anymore.
My external hard drive was under warranty, so I'm getting that replaced. It's not one that has it's own power source, and I had to hook it up via a USB cord splitter. Nintendo said these hard drives could fail from time to time with the Wii U. So if that is the problem, and a new hard drive suddenly solves all my problems, then Nintendo has some explaining to do.