When a pre-lit Christmas tree is not working properly, it may be due to one or more of the light strands that have malfunctioned. Here are a few steps you can take to troubleshoot the issue and fix the lights: 1. Inspect the light strands: Look for any loose connections, broken bulbs, or frayed wires. If you find any of these issues, replace the strand or repair it. 2. Check the power source: Make sure the outlet you are plugging the tree into is working properly.