As a last resort, try a Factory Default Reset as follows:
Power off the Time Capsule for a few minutes
Hold in the reset button first, and keep holding it in for another 9-10 seconds while you simultaneously plug the power back into the Time Capsule
Release the reset button after the 9-10 second hold and allow the Time Capsule to restart
With luck, the Time Capsule will stay solid amber for about 30 seconds and then the light will turn to slow, blinking amber about once per second
If the light stays solid amber, this unfortunately is a sign that the Time Capsule cannot get out of startup mode, almost always because the hard drive has failed....or..... the internal power supply has failed.
In either case, the Time Capsule will likely need to be replaced.