I completely understand how you feel. I've been going through the same thing for 2 1/2 years. It's increadibly frustrating to go into an interview and know you nailed it, then never hear anything back, not even a form letter, and to not have anyone respond when you try to contact the interviewer. And no one will ever say why you weren't selected to move on.

Hang in there. Hopefully your luck will turn around.