Help! Iphone 3GS will not charge or power on.

My battery drained complely yesterday after display a 2% charge. After shutting down, it displayed the loading symbol for an extended period until finally shutting off completly. Since then, I have connected the phone to my usb plug/desktop (not in sleep mode). When I press the home button it displays a low battery for a few seconds until the screen goes blank. I've had it connected for several hours but it has not charged any further nor will it power on. Any suggestions? Please help!!