Burnt-out Christmas lights can be a common problem, but there are several ways to find the source of the problem. First, check the fuses or circuit breakers to make sure they haven't blown. Next, check the light strings for any visible signs of damage, such as burnt-out bulbs or melted wiring. Finally, check the electrical outlets for loose or faulty wiring. If you're still unable to locate the issue, it may be best to call a professional electrician for assistance.