Please help: My Lumia 800's frozen up and won't respond.

Hey.

I got this Lumia 800 from my brother (who got it for review) and have been using it for more than a month. Till now I hadn't faced a single glitch.

Just a few hours ago I was typing out a text to a friend while listening to music with my earphones plugged in when the device vibrated once (in hindsight: this vibration was similar to the one the device makes when it was powering on/off) and...that's it. It froze.

I can still see the screen I was on when this occurred (the messaging screen) because the phone's stuck there. I have tried the three keys below the screen. They don't respond (don't even buzz/vibrate like they usually do). The screen is unresponsive. Nothing happens when I press/hold the buttons on the side (including the power button). I have tried removing the SIM card, but that did nothing. I have tried charging the device (I dunno why. I was out of ideas.) but even that accomplished nothing.

Right now my only strategy is to wait till the device's battery runs out and it shuts. But I don't even know if THAT will happen for sure. Can anyone here suggest something? Has this happened to you before? What do I do?

Any help would be highly appreciated.