Few simple steps to bring your phone back to life
1) Turn off the phone
2) connect the phone on dfu mode ( press and hold home key while phone connect to the PC) : iTunes required.
3) Open below path and delete firmware file (*.ipsw file)
C:\\user\user name**\appdata\roamin\applecomputer\itunes\iphonesoftwareupdates\ and delete *.ipsw firmware file
* PC user name is requred
or type .ipsw on search option and you will see the relevant firmware file
4) Restore the iPhone via iTunes as usual