Consult your local pool professional or click on link below for detailed instructions on replacing the lamp.
The Ballast is bad. There is a date on the underside of the unit and if it is newer than 1/10/15 then that ballast is replaceable. If it is older the Clear O3 unit must be replaced.
Note: the bulb is still good and can be used for replacement after the 13,000 hour life span is over.