The green LED on the adapter indicates that both the hardware and the software involved in the functioning of this device is working properly. It remains steady when nothing is changing on the screen and blinks when data is transferred through the adapter.
The green LED on the adapter does not light up when:
1) The unit does not receive enough power because it is plugged into a port that does not provide the required 500mA of power or because of a failing USB Cable
2) Display to that monitor is disabled
3) The driver is not installed or is corrupted
4) The unit itself has failed.