This a messed job or is there something we don't know about?
There is something YOU don't know about.
As Arakon said, if you can boot to Xell or Xellous, the JTAG wiring is all good.
Your customer is using alternative wiring with an SMC that is configured to use that alternate wiring.
You have wired it back to the original method, but have not reprogrammed the SMC so it won't boot.
I suggest you take a look at thishttp://www.xboxhacker.org/index.php?topic=15214.0
and consider putting the wiring back the way it was to get xell booting again at least.
Now, to get back at the original problem, you need to provide more details. Did the console work previously or did the customer never successfully complete the hack? Does the console report an error?
if the customer never successfully complete the hack they probably try'd to install freeboot and didn't build their NAND properly.