Were there any loose parts? Also I doubt if Nikon would fix this if you opened it up, but you can try.
I've been sitting here for like 5 minutes trying to think about what can go wrong, and I only came up with, anything really. Well of course the problem has to be in the circuit because the flash doesn’t even start up.
You’re best bet is buying a third party i-TTL compatible flash, or a used SB-600. You can also try to send it in to Nikon