My iphone is not turning on after failing to reboot it?

I have an iphone 4 and jailbroke it last week, i tried to update somethin on cydia and then it said to reboot it, i tried rebooting it but failed, the iphone has a blank black screen now and i don't know how to restart it

Hold your lock and home button for a while. Also are you Killian Byrne from Milford, CT?

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