iPhone stuck on lock screen? Buttons don't work?

So, 11 minutes ago, I guess, I was just opening my iPhone 4 and the slider got stuck at the end. Now no buttons work, nor the touch screen, and it still says 6:18 pm...now it's 6:30. The slider is still at the very right of the bar, as though it's about to open, but it isn't. I tried plugging it in to my computer with the USB and it says in iTunes that is "cannot connect to iPhone because there is an invalid response" or something like that. So I have no idea what to do.... SOMEBODY PLEASE HELP ME! I need to use the phone immediately! I can't do a single thing!