I would suggest practicing getting to and maintaining an altered state of consciousness (through meditation, trance, hypnotism). Also, i think with your problem it would be a good idea to maybe try another method. Try using the dream state method, in which you lay on your back and let your mind get to a state in which it starts putting of random dream-like nonsense. Once you get to the beginning of the dream-state, you will know that you are in enough of an altered state of consciousness to project. Try to maintain the dream state (to some extent, don't get stressed if you stop seeing the dream scenery because it doesn't matter, but it can help if you need it). When I started out I would practice moving the limbs of my astral body out until I moved onto my head.
Here's my technique if you'd like to give it a try:
-Meditate until the whole body is relaxed and thoughts subside
-Lay down (belly-side up) and rest until the dream state comes about
-Tingling sensation and separation
Also, it may just be taking a while!