iPhone doesn't charge

Iphone 3GS doesn't charge when I connect it to a network adapter or to a laptop. Only ocassionally, it gets connected indicating charging but it is unsystematic. The chargers I tried with work perfectly with others iPhones.

If it may help, my iPhone was dropped couple of times. Also from my observations, I think sometimes the iPhone might charge while it shows no charging.

Any help would be much appreciated

Thanks in advance