Then I would focus on the lower LED-strip.
- Check that it is oriented correctly (signal in / DI to the right and GND on the bottom.
- Measure connection between DI on the LED-strip pad and pin2 on the arduino. (using continuity tester on a voltmeter)
- Measure connection between +5v on the LED-strip and VCCon the arduino
- Measure connection between GND on the LED-strip and GND on the arduino
You can also connect it to a computer with a DAW software running (handling the midi events), then the tx led should flash for every key press. (Verify this behaviour first using the working midi keyboard)