My iPhone 4s shut off and won't turn back on? My lock button is broken, so I can not reboot it.

You can try and let the phone sit for a period and then try connecting it again to the power source. If that doesn't work, I cannot think of another solution. The only way to reset the phone in a case such as this is to old the sleep/wake and home buttons together until you see the Apple logo and then release. However, since you say the sleep/wake button doesn't work, then there is no alternative. I'm puzzled though when you say that you locked the phone and walked away. If the lock button doesn't work, how did you do that?

Okay, I understand that. However, like I said, the only way to reset is as I described. You can let the phone try and run the battery dead, then plug it in and see if it will restart.

You're welcome.