iPhone 4 blank screen - restore does not work

My iPhone 4 has a completely blank black screen. I have tried turning the phone off/on and holding down the home and power button for 10 seconds (I have tried holding down for about a minute, just in case...)

When I connect the phone to my laptop it makes the sound that it does when it's recognised a device, so I know the phone is still functional, I just can't see anything on the screen.

At one point when trying a variety of buttons, the voice control function kicked in which again confirms that the phone is still working.

Anyone have any ideas? I have only had the phone for 1 week.