I had faced this problem after my iphone 4s was water damaged. I opened it up and cleant the dock with alcohol( Please use a better chemical to clean) It worked for few hours and then again got docked( No sound on ipod etc ) I again opened it up and cleant it and let it dry for some time and now its working fine no problem at all. There is also a chance of the dock connector not functioning. You can easily replace it if possible and your problem will be solved
