I'm not sure what happened to me a few days ago, for the first time, but it was on when I last left it and when I came back, it appeared to be off. Would not start at all. So I pulled out the battery and put it back in and it worked after that. Not sure what caused it, but it was the first, and last, time it happened to me.
Battery-pull seems to be the answer. If not, pull the battery and plug it in to the wall charger without the battery and see if that works. Not sure if it's dangerous, but it may be like a jumpstart, after which you can insert the battery while plugged in to the wall, and then pull it off charging to see what happens.
After typing all this, I realized you were talking about the lock screen locking up, not the phone being unresponsive.
Battery-pull seems to be the answer. If not, pull the battery and plug it in to the wall charger without the battery and see if that works. Not sure if it's dangerous, but it may be like a jumpstart, after which you can insert the battery while plugged in to the wall, and then pull it off charging to see what happens.
After typing all this, I realized you were talking about the lock screen locking up, not the phone being unresponsive.
