charge the camera with a regular cell phone adapter. USB on the PC doesn't charge the camera!
With a cell phone adapter (iphone, Blackberry, Samsung) it takes about 45 minutes when my camera battery is completely empty. Be sure that the red light pulsates when charging. If it stays solid red it doesn't charge. Had the camera the whole night on the USB port the first day only to find the next morning it was completely utterly empty. It also charges quite quickly in the car with a car phone adapter.