Never open a hard drive that you plan on using, unless you're a professional in a sealed environment. Even then it's risky. Now that your hard drive has been dropped, damaged, and opened, that drive is a very unreliable. Too unreliable. If the data on it is that important, than you'll have to send it to a data recovery place, which might charge a pretty penny. But I don't recommend doing it yourself if your data is important. A word of advice: don't delete the data off your computer until has been safely transfered to another computer.
Hope this helps.