Battery fully depleted, won't turn back on
So I fully depleted my iPhone by this morning, and when I came to work, I plugged it in to get it charged back up......two and a half hours later, it's still showing the "dead battery" screen. I've tried resetting it by pressing the power button and the main button, which allows me to turn it off entirely (screen goes blank), but when I try to do the reset a second time, I just get the "dead battery" screen again. It's plugged in via USB to my computer, but the computer can't see it, it's just considered charging, I guess. Any recommendations would be greatly appreciated.
3GS, iPhone OS 3.1.2