The key to making biscuits, is making sure that the butter is cold when added. If the butter melts while mixing, the dough will become ladened with fat and the biscuits will not rise. Also, make sure your oven is at the proper temperature before baking. Another reason may be that your baking powder has expired. A great way to test this is to add a tbsp to a small bowl then add some hot water. Fresh baking powder will begin to bubble as it releases carbon dioxide.