How is the high beam? Same thing or not? Did you recently do any mods to your electrical system? If the High beam side is ok, try switching the ballasts. The lower priced HID ballast are known to flicker after some time.
I haven't had a chance to swap ballasts for a test yet. The Low beam ballast doesn't fire up at all. Could there be a wiring/connection issue that would affect the low beam without affecting any other electrical system?