08 XK Limited will not start.

[Matt]

I knew it wasn't the battery! Told you it had something to do with the starter

Nooo, you said "it is the starter" not "something to do with the starter"

It could still have been the battery when you said it wasn't the battery. Lack of being able to jump start it and the lights still working doesn't mean anything on newer vehicles. I believe post #6 and #7 were right on. Proper diagnosis >>> guessing lol