Ahh!! why doesn't my slide to open on my iPod 4g unlock?
if it keeps happening go to an ipod store and consult one of the people there
Just shut down your iPod and turn it on again
If your iPod Touch is locked and you cannot slide the unlock button, you might want to take it to an Apple store to have it checked out for repairs. If you warranty is still valid, this process will be free.
if their are no cracks it is possible the touch screen technology under the glass could have been damaged. I would go to the Apple Store and have them look at it