Check to make sure make sure your garage door spring(s) are ok first. Pull the emergency release with the door in the down position, to disengage the garage door from the opener. Try lifting the door by hand. The door should open easily with little effort.If the door is hard to lift, the spring(s) mihgt be broken or may have become fatigued. You need to contact a qualified garage door company to fix this situation. If the door moves up easily, re-engage the door to the opener and try turning the open tension up just a little bit. If you moved the open limit already you have to move the back to where it was originally to prohibit the door from opening to far before activating the opener. If the door is still not opening fully, then try adjusting the open limit and open the door again. If this still makes no difference where the door stops then move the open adjustment back to where it was (counting the turns), then try turning the open tension adjust up a little more and repeat the process. If this does not work for you, there might be an internal problem with your opener and sometimes it is less expensive to replace it rather than have it serviced.