Flashing green is symptom of an internal problem on the Express....likely the power supply.
As a last resort, try a Factory Default Reset to see that will get the Express back to new settings, so that it can be reconfigured.
To perform the Factory Default Reset.....
Pull the Express from power
Wait a few minutes
Hold in the reset button first, and continue to hold it in for 9-10 seconds while you simultaneously plug the Express back in to power
Release the reset button after the 9-10 seconds hold perid and allow a full minute for the Express to restart to a slow, blinking amber light
Now try to reconfigure the Express again.
If the indicator light still stays flashing green after a few tries with the Factory Default Reset, the Express is defective, and will need to be replaced.