headlights Xenons worked...then didn't....now do again? WTF?!

So I just retrofitted OEM xenons into my halogen housings. They worked great...and then a week or so later the passenger side stopped working. After a few days of not working, I decided to dig into it. First I checked to make sure the plugs had not come loose. Then I tested the bulbs; they both work. I swapped igniters; they both work. So I swapped ballasts, figuring that must be the problem........but they both work. So now I have torn apart my headlights only to find that they magically work again. Anyone have any ideas? If I put them back together, and they stop working in another week or two, I'll flip out.

Anyone had this happen before?

could be a loose connection with the car. or the connection with the bulbs wasn't tight. if everything works, most likely it's installer error