I can think of two answers, I suspect the first is the one you want:
The device is stuffed (sorry, can't type the Kiwi accent). You need to go out an buy a brand new and wonderful Kobo Glo.
That's what you want to hear isn't it?
If it isn't, you can try the home+pin hole reset:
- Firstly make sure it is really off buy holding the power button in the off position for 10 seconds.
- Hold the Home button down and push something into the pin hole until you feel it click. Release that but keep the Home button down until the light at the top starts flashing.