I have had a line 6 dl4 for a little while. Yesterday when i was fiddling around with the looper setting there was no delay. Nothing. The delay on the other settings was fine...the delay knob worked perfectly. I'm wondering if i may have pressed a certain series of buttons or whether it is actually broken. Anyone know what to do or seen this kind of thing before?
Try resetting it for factory settings:

Hold the far right and far left switches down whilst plugging in the left/mono guitar input