Nikon speedlight issues

[4Lmike]

My SB600 has suddenly stopped working. Everything comes on as normal, except the thing doesn't fire, not even when I press the test button. It just makes a click sound. Any ideas? Is it likely it could be repaired or is it buggered?

[Simpo Two]

I wonder what's clicking?

Might be worth a call to Fixation (just to make sure they can't fix it and you need a new one...)