Sorry to hear you are still having troubles.
The 74AHC04 is a CMOS version of the 7404.
CMOS is better at sinking current than sourcing.
This means it is better at providing a ground than a source of power.
You hooked it up alone and watched it change the output as you changed the input, right :?:
What is the LED resistor's value :?:
You probably only have 8 mA to work with.
When you connect the LED anode to the 74AHC04 you use it as a source of power.
Try reversing the LED circuit:
Connect the LED cathode end to your 74AHC04 and change the current limiting resistor to the positive power rail.
A positive input to the 74AHC04 gate should now provide a output ground to sink the current, lighting your LED. :idea:
The 74138 is a more complex decoder with several pins that need attention before it will do much for you.