First I suggest a hard reset. Hold the power & home button until you see the logo and then release. If this does not solve the problem, then I suggest making a Genius appointment to have you phone looked at.
If only your home button works, then you can't do a hard reset. You can try a soft reset by going to Settings > General > Accessibility > Assistive Touch. > device > long press on "lock screen". > slide to power off.
Or let the battery drain down until it shuts off on its own.