The 8830 had some issues with the USB port; perhaps you've got a loose connection? Though I assume if that were the case, the phone wouldn't indicate that it's charging.
Are you with any other 8830 users? Perhaps you can switch batteries and see if your battery charges in the other person's phone.
Sounds like the juice isn't getting from your USB port to your battery...I'd guess there is a hardware issue there somewhere but don't know enough to diagnose it beyond that.