a question about metal halide bulbs

[Brighteyes_13]

so christmas was good to me, got a used pair of ballasts and bulbs for my fishtank.

everything wired up easily, and the switch was thrown. both bulbs began to warm up and i was feelin pretty proud of myself.

after a few mins one of the bulbs began to flicker, almost strobelike, then after a few mins of the flicker it went out only to warm up again in a few more mins and restart the process. i turned off the setup, let cool and switched bulbs, and the same bulb (other socket) again flickered.
i was told the bulbs were only used about half a year, could it just be from not being used for over a year? or is the bulb dead?

anyone else have this happen before? any comments would be really apreciated