Check the synch by removing the lens, opening the back and firing the camera and flash in a darker room using the settings you have been using. If the synch is good you should see a very bright image looking through the open shutter.
A couple of things to double check -- don't take offense if they seem way too obvious: 1) The Nikkormats synch at 1/125. I always assumed that meant 1/125 was the top synch speed, but who knows whether 1/60 doesn't work properly as the synch speed. 2) what aperture is the lens set at? If it's at f16, say, the flash may not throw enough illumination to give a good image.