Something to remember is that unlike a PC or a MAC, if the Kobo eReading application crashes, it is more than likely that the screen will stay looking like a book IS being read.
There is a long standing intermittent issue I still see on my Touch where the screen stops responding to presses. At least on the Touch I can then press the button to return to the main screen (but this too is non responsive).
At this point all I can do is to turn the unit off; this requires a LONG hold over of the power switch. I can't remember if the screen changes at this point to the power off or not. Finally, a power back on and the device is back working again.