What system menu version is the wii on now? What was it on before? This can be found in the wii settings.
Do you know what kind of chip you have?
What is the region of mario kart?
What about your other original games? Is it possible they are a different region? USA ntsc or Euro pal.
It sounds like your wii was updated to 4.2, and mario kart is in the region of your wii, while all your other non-functional games are out of your wii's region. If this is the case, your wii is not bricked, but there is nothing you can do about it at the moment. Perhaps in the future there will be a firmware update for your chip with a fix, but at this time the only solution is to softmod or only play games in the wii's region.