An old thread, but bumping it since it happened to my KS16 today.
I rode it back from work, and wanted to turn it off so I could carry it up the stairs to my house, like I normally do. Pushing the on/off button made the wheel lose balance, but the wheel itself "locked", so could not move the wheel manually - and LED lights didn't turn off. I couldn't turn the wheel off at all.
After holding the wheel upright with the handles and wondering what to do for about 30 seconds, it started vibrating for a split second, then shut off - for good.
Now I can't turn it back on at all.