Stan Keenum, of course your ISO setting is around 400. the flash will not work if your ISO setting is high. I would think that if nothing has happened to your camera and this just came up, that the first thing I check for would be the main condenser and the wiring to the DC-DC board. Also check the popup switch. You can download the service manual for your camera [http://www.keepandshare.com/doc/3342678/nikon-d50-service-manual-pdf-december-9-2011-10-23-pm-14-6-meg?da=y|from here]