sounds like you have a stuck ferment. Identifying what may have gone wrong is probably easier than trying to make it ferment more. To get a few more points out of it, you might be able to rouse the yeast by swirling the fermentor and/or warming it up if it got too cold.
To figure out why it got stuck, the following questions are applicable:
What yeast did you use, how much did you pitch, did you oxygenate your wort, and what temp did you ferment at?