you still see an active video signal, right? Your TV detects there's something?
if the tv doesn't even see the signal, it could be a video issue.
is your wiimote sync ?
I don't know how far the console boots when it's a bluetooth module problem.
if priiloader doesn't launch, there's not much you can do.
ask your friend what he did, if he tried to install or replace anything, or launched homebrew he didn't know what it was used for. Maybe even installing wad files with a manager ?
maybe he replaced his system menu with another wad file, replacing priiloader and preventing the console from booting if the console doesn't have the needed IOS.
you could reflash nand using a hardware device, if you did a NAND backup and know how to solder.