Astral Projection...have you? Questions about an astral projection "mental block" also...

I've been studying the art and science of astral projection for years. I've never been able to do it "on command" using any of the hundreds of varied techniques described and taught in numerous books and websites. I've been able to separate parts of my body on command, but that's it. I used to be able to "vibrate" my body a few years ago, at first using meditative techniques, and eventually "on command," to begin astral projection (when I was able to consistently separate parts of my body), but for some reason, for the past two years, I can't even do that anymore. It's like there's some kind of mental block or something. I've tried all the old methods, visualization, etc., and even tried some of my own to no avail.

I have only fully astral projected twice, but not on command. Occasionally, I suffer from bouts of sleep paralysis, they started when I was 15. They used to frighten the hell out of me, but when I started studying astral projection, the sleep paralysis intrigued me. My only two true astral projections occurred when I awoke in a sleep paralysis state: I would realize what was happening, and was able to immediately separate my astral self and "travel" around... The first time I was able to go to my dad's living room, and I saw him watching a football game and yelling obscenities and certain phrases at the TV. The next day I asked him about it, repeating to him what I heard and saw and he was in awe with my accuracy even though I "wasn't there" physically...anyway...Like I said it's only happened twice and only during a sleep paralysis episode...

So I'm just curious if anyone has any tips or suggestions for me to be able to project on command? I also want to know why I can no longer even get to the "vibration" point anymore! Any thoughts appreciated!