Sigma EF 500 DG Super flash?

Help troubleshooting Sigma EF 500 DG Super flash on a Nikon D3200. The flash won't go off. But it works (as it flashes when i test it [pressing "test" button]. Tried it on manual settings, won't work.

Any help much appreciated.

Do you have transmitters? Is flash turned on on your camera? Otherwise, I don't know

Here's a checklist of what you can do:
Are you sure this EF 500 has the right (Nikon) flash mount with all the contacts in the right place? Sigma also made EF 500s flashes with mounts specifcially for Canon, Pentax etc.
Have you checked the flash contacts (on camera as well as flash) for dirt or corrosion?
Are you using a fresh set of batteries?
Does the display on the back of the flash unit work?
Have you cycled through all the flash modes (mode button) to see if there's one that does work?