Try removing the battery if you can or hold volume up and power for a round 15 seconds - If that fails then unfortunately you will have to perform a repair which results in all apps and data been lost
To perform a repair make sure your phone is unplugged and turned off
Start PC Companion and select Support zone then Update my phone/tablet then in Blue select Repair my phone/tablet and follow the on screen instructions - When prompted hold volume down and connect your USB cable
