The laptop itself magically started working again after a few more cycles of disassembly and re-assembly. No clue how, but it runs now and seems to be back in good health. Didn't do anything differently between the times it failed to power on when reassembled and the time it just started working again, but it works now.

Laptop refuses to power on at all after this, just gives a 6 second blink of the power LED and the F12 LED when the power button is pressed. No screen backlight, no fan noises, no light under the power button... Anyone know what could be wrong? All ribbon cabels reseated properly, and used ESD protective wrst strap during procedure throughout.

Laptop refuses to power on at all after this, just gives a 6 second blink of the power LED and the F12 LED when the power button is pressed. No screen backlight, no fan noises, no light under the power button...