Press and hold the Home and Sleep buttons, simultaneously, for about 10-15 seconds. If that does not resolve it, it could be the battery. Plug it in to a wall outlet for a while and see if that was it.
HI, mine has frozen/locked up too. I tried the Home and Sleep buttons but no effect. I got a low battery sign so plugged it in overnight, no change. Plugged it into iTunes, still nothing. Any other suggestions ? Thanks