Counter which counts to 5 and then turns on a led
You probably want to put a resistor in series with your LED.  It may be dragging the output of U3:A down so far that U4:B isn't seeing a high on its input.

Of course, if you reset all three the LED will go off immediately.  However, you could reset just U1:A (if you really want it to stay at 6 instead of 5) or more generically you could tie J and K of U1:A to the output of U4:B so they both go low once you achieve whatever final count you set it to.