Someone may have used the switch to turn the lights off and forgot to turn it on. So, you should confirm if that is the case. There is a probability that the battery did not charge to full during the day, even though there was enough sunlight. In this case, you should clean the solar panel to prevent shading. The battery may be damaged such that it is unable to store enough power for use during the night. If that is the case, you should replace the battery.