Since it's a FiberStar system, all the electrical parts are in the light box head. I think those lamps are metal halide, so they have a ballast. It could be as simple as moisture getting into the box, or it could be the ballast going bad.
Turn the power off and open the box. Don't touch the lamp with your hands. You don't wan to get oils on the lamp.
Look for any moisture in the box and on any electrical equipment in the box. If you find any moisture, dry it off and close the box and try it again.
If you don't find any evidence of moisture, you may need to troubleshoot it. There is a troubleshooting guide in the manual. If you don't have one, you can download one for it.