I have the exact same symptoms.
Latest advice is maybe PMU Chip needs reset by holding down Power button 5 seconds. I have not tried that yet.
Also the ribbon leads are so small maybe as suggested there could be a failed connect.
It was the brief RED Diode at the power connector that interested me, I had the same coupled with a brief 'squeal' from inside.
After my last battery went flat then I have been unable to start up the machine.
Do you have any update on the issue?
Dave