All of my ideas include hooking up different things, but if you're out of ideas:
Do you have an extra QD to try?
If not, can you remove the QD from the line and open the tap to see if you get flow through the line to the faucet?
Do you have a cobra tap or something similar that you can connect to the keg?
With a few of these it seems you could at least narrow it down to something between the dip tube and the exit point or something between the QD and the faucet.