I had this happen to me last night (iPhone 4S) and my top button has not been working for some time.
I could still use Siri (speak to her and hear her but no see anything) so I knew it was just a screen issue.
I read through many MANY forums the general consensus is to restart the phone, but without one of your buttons working that is difficult. For me it was a combination of solutions;
One person suggested holding the home button and the volume + button together for 25 seconds which can force a restart.
Another suggested running your battery flat, again hard to do when you can't access the screen. So I called my phone A LOT and talked to Siri to run it down.
I think it was a combination of both things because my phone eventually turned itself off. I only know this because Siri stopped responding.
Then I plugged it into a power source and the empty battery icon appeared. About 10-15mins of charge and the screen turned on.
I hope this helps someone else out there.