Press and hold the Sleep/Wake button for a few seconds. Wait for the iPad to display a slider on the screen.
Once the slider appears, follow the on-screen prompts to slide the button from the left to the right. Wait for the iPad to turn off completely.
Press and hold the Sleep/Wake button until you see the Apple logo. If the iPad appears frozen, you need to use a combination of the Home and Sleep/Wake buttons.
Press and hold the Home and Sleep/Wake buttons for at least 10 seconds. This combination should end the frozen state and power down the device. Note the circle of dashes on the screen, and wait for the iPad to shut down.
After the iPad shuts down, press and hold the Sleep/Wake button. The Apple logo should appear on the screen after several seconds. Once you see the logo, release the buttons; the iPad should restart after the logo disappears.