Try a Factory Default Reset as a last resort.
Power off the Express for a few minutes
Hold in the reset button first, and keep holding it for another 9-10 seconds while you simultaneously plug the Express back in to power
Release the reset button after the hold period and allow a full minute for the Express to restart
At this point, the light should be flashing amber slowly, indicating that the Express has successfully been reset
If you try the Factory Default Reset a few times, and the light remains solid amber, the Express is defective and will need to be replaced