Aw,it sounds like your bamboo has stem rot which means it's finished. With bamboo you have to dump the water and give it fresh water every day other wise it gets stagnate and rots away. There isn't much you can do at this point if the yellow is down in the roots. You can try to save it by cutting the yellow part off and taking the green and starting over but it most likely will not re-grow the roots and will die.
Heat, cold, lack of water, not clean water. The chances of saving it are not too high, but you can try. Put it in a glass of clean water and keep out of sunlight. If the stalk and leaves are yellow, it's not going to be able to be saved though.