Sounds like too many watts going through the switch. It is important to know what is on that circuit. Sometimes things can be plugged into an outlet that drag a lot of wattage and then turning on the light(s) causes the circuit to overload, but not quite enough to blow the breaker.
I would make sure that that circuit is not overloaded. Find it in your breaker box, identify what is supposed to be on it, make sure your light bulbs are not over the rating (example: the circuit has 4 100 watt bulbs and you changed three of them to 120 watts)and other appliances, etc. are not plugged into the same circuit. If you make sure you are running the correct wattage bulbs and nothing is plugged in, you may have a short. I would have it checked out by an electrician soonest to be safe.
You can check the circuit by throwing the breaker (shutting it off) and see what stops working.