I had the same problem. The screen went dark on my iPhone, and the power button hasn't worked in a year. When this happened with my Android phone, I just removed and replaced the battery. Since I could not do the same with my iPhone, I thought that I would have to trash it. So I put the phone in a ziplock bag (to help protect it from condensation in case this actually fixed the problem) and stuck it in the freezer, hoping to kill the charge on its battery. I had no other way to drain the battery.
Remember, I thought that I would have to trash the phone - I was not about to pay for the repair of a 2+ year old phone with 2 problems. When I removed it from the freezer more than an hour later (I did not time it), I pressed the Home button and nothing happened. When I plugged in the charger, the battery indicator came on and indicated that the battery was empty. About 1 minute later it started right up. It worked fine for about 2 weeks, until I tried to use an app I had not used since the phone went bad. The app locked my phone again. I will be deleting this app after I remove my phone from the freezer.