If you've readjusted the opener, and it still isn't working, you need to have a trained door technician come out and adjust the tension on your springs. To determine this, pull the red release handle to disengage the opener from the door, and try to lift your door by hand. You should be able to move the door easily, and it should stay at the half open point without falling or rising. If the door is hard to move, excessively heavy to lift off the ground, or will not stay open, the door itself is the culprit. If the door is fine, the opener will need to be serviced.