Are you sure there were no blockages in the new line when you put it on?
Do you think you might have installed it incorrectly somehow?
If there's no blockages and it is installed properly, then you might have an air lock. You'll have to find some way to force the fluid through the system. That means sucking or blowing.
If you have a vaccum pump, put it on the open bleeder nipple and pump until you get fluid. Or put a clear hose on the bleeder and suck on it while pumping the pedal. (Yep, you just might get some in your mouth this way.)
Or, apply pressure to the reservoir and force the fluid through. Or rig up a large syringe or turkey baster with a hose and try pumping fluid through the new brake line, then re-attach it to the master cylinder.
Hey, you asked for ideas...