Having gone through many G4 Powerbook dismantlings myself, your friend might have not properly re-connected either
1) the keyboard ribbon
2) the power cable connecting
It happens to me a few times too - dismantled everything, then only to reassemble back and find it's not powering on.
At this point in time, since you have no "eyes-on" as you said, I recommend that you suggest to your friend to once again dismantle everything, and reassemble everything, according to schematics and pictures that could assist him (choose the appropriate model for his 17"). However, when it comes to finally reconnecting the keyboard - do not fasten the screws - just connect the ribbon and press the power button to ensure it is working. If not, troubleshoot from there by reseating RAM, plugging in power (be sure to ground yourself), etc.
Cheers, let us know what happens.