All discs showing up Invalid

I bought a used WiiU from GameStop a couple of months ago and a few games to go with it, to go with my large catalog Wii. I've been happy playing my Virtual Console games and Mario Kart 8 with my son (built in digital copy), but yesterday I wanted to play some Wii games and maybe Pikmin 3 or Mario 3D World. Every disc I tried, whether Wii or WiiU, gets an invalid disc error. I've tried 10 different games, all the discs look fine, and all the Wii games work no problem in my Wii. I've seen this be an issue with other people with a couple of games here and there, but not a single disc in my collection works. I've seen people mention a cleaning disc, but it doesn't look like it's available anymore. Are there any other methods I should try? I'm pretty bummed, and I'm worried about losing my data and VC games if I return the unit for another.