When I started up Mario Kart 7 it froze at the Nintendo 3DS logo but is continuously doing the red wave thing. I can't even press the home button or turn the system off.
eh that happened to me on my 2DS. It's nothing to worry about, but the way to turn it off is to either take out the battery or just wait until the battery runs out. You should then update your system or contact Nintendo if it keeps happening.