Green, I think that you are missing the point of this thread entirely.

The thread is about the inbuilt flash on one particular model (D90) failing to lock into a closed position when manually lowered.
It isn't about the flash failing to work.

It seems to be a reasonably common problem with the D90. Similar problems have been encountered on other Nikon models.
The problem appears to be that the closing lock was not optimally adjusted at the time of manufacture or has moved out of adjustment during normal usage.
The "cure" is a non invasive adjustment procedure by means of a screw that is accessed purely by having the flash in the open position.
That screw is purposely put there to allow for easy latch adjustment without having to perform any internal work on the unit.

Rather obviously if the camera body has suffered damage from impact and the operation of the flash latch is compromised to the point of needing disassembly and parts replacement then a trip to the camera doctors may be in order but the details here are presented purely as a first step adjustment method to rule out further work. There have been plenty of people that have satisfactorily performed this step and saved themselves time and money and avoided any internal probings.