Chances are that the glass vial that contains the mercury has gotten broken, or a connection inside the light housing has corroded. Look for a crimped seam or some other way to disassemble the light to inspect the inner workings and gently unroll the crimp for access to the interior. I don't think those lights were designed to be repaired, but it had to be assembled somehow originally.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!