My Fluval lighting unit has suddenly stopped working. It flickers when I switch it on, but the lights won't stay on, and the little red light on top near the switch flashes. What's likely to be wrong with it, and how can I fix it? Admittedly I haven't tried replacing the tubes, but as there are two of them I feel it's unlikely they'd both have failed at the same time. (I never replace them together). Thank you.