Why do headphones only work when half plugged?

Why do headphones only work when half plugged?

I purchased and installed headphone jack.

ANSWERS:

"Unfortunately, it sounds like you received a broken jack! There's an outside chance it could be your motherboard, but I'd say buy another jack on eBay, they're only 3 dollars or so. It's worth a try.

cheers!

-tabormeister"