u probably had a nand backup for a different console. or ur console was flashed with the wrong nand n thats why its not booting. but if a professional as u say is working on it. he should be able to get it up n running if its a nand problem.
Please elaborate with one scenario, if my son or his friends might have updated the dash with the updated dashboard from DVD or CD, then also nands won't match? As this is the only possibility left, as I have enabled MAC filter in my wifi router and only my 2 mobiles and 2 laptops can connect to my wifi router, Xbox can't connect with the wifi modem. Even if it can I would require Xbox live account to update my dash, and I don't have any Xbox live account, I used to connect my xbox to my wifi modem only to update DVD covers from some site, I don't remember its name.
Secondly if this is the scenario that my son or his friend might have updated the dash, what are the chances of my xbox getting back into life? I mean is it still possible to fix it or it is gone for ever and I should start selling its parts separately like its adapter and kinect.