If your iPhone is showing a black screen that never goes away, you should try resetting it or putting it into recovery mode.
If your iPhone won't turn off the usual way, you can force restart it with a button combination specific to your iPhone model.
Hosted on MSN
How to Fix An iPhone That Won't Turn Off
The issue can involve a software problem, a damaged screen, or a broken button An iPhone that's stuck in the on position is a rare situation but if it's happening to you, here's what's going on and ...
Some results have been hidden because they may be inaccessible to you
Show inaccessible results