Flash back to GB from ICS on Vodafone Sensation z170e

[habboc]

i had a software update(Android 4.0-ICS) notification on ma Vodafone Sensation, i downloaded and runned it and now screen touch has become completely unresponsive. all function keys dont work except for the power button.is there any way to flash back to GB.......step by step preceedure will be appreciated. thank u