How to find a short on the motherboard

Hi there, we are trying to find a short on one of our client's motherboards, we do not know which component causes a short, we do use a multimeter but it always shows zero since there is a short all over basically when we connect a multimiter to the postivie and the negative end it always gives us zero ohms resistance since it is shorting, but where, that we can't figure out. Any help would be appreciated on what equipment to buy,
we heard something about 4 wire digital multi meters any one knows if they work, and where to get them?
Thank you
Alex