Gwen Wester, there are a couple of things that you wan to go through. Make sure that you have the right battery. For the 3GS the number should be APN:433, 434, 435 ending digits. Make sure that your USB cable is working. Try and charge the battery on an AC adapter since it provides a higher amperage than a USB port. This is just in case your battery may be to discharged, to charge from a USB port. Check the dock connector, make sure the pins are straight, not broken and no corrosion or debris is present. Clean it with some isopropyl alcohol and a few puffs or compressed air. You can use a multimeter to check if your logic board receives power when it is plugged in. Check the traces for continuity. You should get no less than 3V on the battery contact. If you do not have anything or just very low voltage, check the fuses on the logic board for continuity. Attached image will show you the location. If it still does not charge, replace the dock connector. Use this guide to get it done. If all that checks out, take a luck at the power management IC and see if that is checking out. The PMIC is a 338S0533. Hope this helps, good luck.