Why doesn't my Nikon flash SB80 not work on my Nikon D80 slr?

I've used that flash on this camera before and it has worked. When i used it today, I went to go push the shutter down, but it wouldn't go down.

The shutter release will not operate if there's no memory card, the needed shutter speed is beyond the range of the camera (like 1/8000th second and your cameras highest shutter speed is 1/4000th second) or sometimes if the shutter speed is set higher than the flash sync of the camera. This is 1/200th second on your camera (page 144 of your user manual)

There may be other reasons why the flash is not working, but you will have to use the trouble shooting procedure.

I have an old SB50-DX snf it works perfectly on my old D100, D200 and my D300.