Could you also try pressing the volume down (-) and the power key together and see if the phone vibrates after about 10 seconds? If it does, try connecting it to a charger again and charge for a couple of hours before trying to power it on.
If this doesn't help though then I'm afraid your phone is in need of service. You can contact your Local support team for more information on where you can find one of our authorised service centers and how to proceed from here.
