When an inverter's lights are on, indicating that it has power input and seems to be in an operational state, but there is no power output, several factors could be the cause.

　　Firstly, a faulty internal circuit breaker or fuse within the inverter might be tripped. Inverters are equipped with these protective devices to prevent over current and short circuit situations. If there has been a sudden surge in current, perhaps due to a short circuit in the connected load or a problem within the inverter's own power electronics components, the circuit breaker or fuse will cut off the power flow. Even though the control circuit of the inverter may still have power (which is why the lights are on), the main power output path is interrupted. To resolve this, one needs to carefully inspect the circuit breaker or fuse, identify if it has tripped or blown, and replace it if necessary after ensuring that the root cause of the over current has been addressed.

　　Secondly, issues with the power conversion components can lead to this problem. The heart of an inverter is the power conversion stage, which typically consists of semiconductor devices like insulated gate bipolar transistors (IGBTs) or metal oxide semiconductor field effect transistors (MOSFETs). If these components are damaged, for example, due to overheating, excessive voltage stress, or manufacturing defects, they may not be able to convert the DC input power into AC output power properly. Although the control signals are being sent to these components (as indicated by the lit lights), the malfunctioning power conversion components cannot execute the power conversion process. Diagnosing and replacing these damaged semiconductor devices usually require technical expertise and specialized testing equipment.

　　Another possible reason is incorrect settings or a malfunctioning control board. Inverters often have various settings for different operating modes, voltage output levels, and frequency. If these settings are accidentally changed to incorrect values, it can result in a situation where the inverter is not configured to produce the expected power output. Additionally, a malfunctioning control board, which is responsible for sending control signals to the power conversion components, can cause issues. The control board may be affected by electrical interference, component failures, or software glitches. In such cases, re initializing the settings to the default values or repairing/replacing the control board might be necessary.