If your computer has crashed and just does not simply respond, even when you press the power button this may help (this does also apply to lots of other electronics too):-
- Hold down the power button (on/off switch) and count to 7.
- In that period of time the device should have switched off.
Failing the above, remove batteries and mains connections for at least 30 seconds.
If this is happening regularly. Please book a time online to troubleshoot this issue further.