Whether you are running Android ICS CM9 on your HP TouchPad or the stock webOS, chances are the touch screen will not work sometimes after the device went to sleep. When you wake up the device, you won't be able to unlock it. Even if you press the power button and show the options, you still won't be able to choose the action that you want to perform.
There's only two ways to force the restart, one is to drain the battery and then restart. That would re-activate the touch screen. But what if you have a full battery? It might take you at least a day to drain the battery. It's either the battery drains or it drains your patience. That's obviously not a very good option.
The better way is to press the Power and Home buttons simultaneously and hold it for 30 seconds until the moboot appears. You can then select the appropriate actions as the touch screen will be re-activated by then.
Source : cyanogenmod forum