Hold the home and sleep buttons down together... KEEP PRESSING until the screen goes black and the Apple logo appears.

Let us know if that helped?

Unless the phone has crashed, just holding down the sleep button until it prompts you to "slide-to-power-off" should be enough.

The above should also work, but it is really designed for when iOS won't turn off normally.

Duh - why didn't I think of that??? My I-Pad often needs that fix, but I seldom ever have anything go cantankerous on my phone.

Great suggestions from other posters. Def try what target practice suggested. Hope all goes well.

Try to factory reset and set it up as new.