Hmm... The only time I've ever personally seen these sorts of symptoms on 550s (and new 250 fixtures for that matter..) was when the voltage on the mains supply for the fixtures was something rather much lower than the fixture was set for.. ;) They just started to fire up, but then just kept resetting with #### displayed on the screen while doing so. Now.. are these two fixtures on the same bar, running off the same hard power supply? Have you tried taking them down, plugging them into an independent (remembering my theatre speak here :o), or some other hard power supply? Are the lamps autostriking? If so, try disabling that then powering them up & seeing what happens. Erm.. Or it could be Gareth's idea, though seeing as its been a fair while since there's been 550s around with that problem, you'd have thought it'd have happened before now.. But you know what its like sometimes with these sorts of things :). Sorry if this all sounds patronising & obvious, but HTH. Tom