Paolo Tauro if your flash does pop-up check on the [post|82997|answer here] It is very similar to your camera. Of course there is also the possibility that it is your Flash bulb so use [guide|32731|this guide] to check on that. If nothing else, teh SM for your camera is on this [[Topic:Nikon D90|this page]] listed under Documents. Of course, I would also try a reset of the setting. Something like this. Place the camera into manual (m mode), scroll with the thumb wheel until the shutter speed is 1/200, press the button on the side of the camera to force the flash up, and then take a picture. This should verify that your flash is truly not firing.