The first thing you need to do is see if the input shaft in the speedo head is seized....a very common problem. If the cable broke, there is a reason for it. You need to find that reason before just plugging in a new cable, or, you may just break the new one right away. Other things to look for would be a kink in the housing, melted housing from being too close to the exhaust, and lack of lube in the housing.
