A beginner lost at sea, Arduino looking at the sun
You'd better post also the schematic, but I'm pretty sure you just messed up the circuit.

I think you just put the ground connection for the LED strip in the wrong pin (AREF). If you look, the top-most blue wire goes to the third pin from above in the right connector (which is AREF) instead of the fourth one (which is GND). Move this and it should work

Otherwise, put the schematic on the question