OK, thanks for the information.
4-5 years is about it, on average, as far as the useful life for the Time Capsule......so that is probably something to consider.
If you are dedicated do-it-yourself type of person, it is possible to open up the Time Capsule and replace the power supply and/or the hard drive. But, having done this myself, I would caution that this is not easy.
You might able to get a clue as to whether the issue is a failed hard drive or failing power supply if you power off the Time Capsule, wait for 15-20 minutes or so, power up the Time Capsule again and place your ear right on the top of the Time Capsule to see if you can hear or detect that the hard drive is spinning. There will normally be a very slight vibration that you can feel when you do this.
If you can hear or feel the hard drive spinning, the hard drive is likely still good and the problem is usually a failing power supply, so that would be the first thing to try to repair, if you decide to proceed.
Keep in mind that even if the power supply can be replaced, that you will still have a 5 year old hard drive installed inside the Time Capsule, and it will likely to be too long before the drive will need to be replaced as well.
A repair shop could handle this for you, but the big downside would that the cost of parts and labor would exceed the cost of a new Time Capsule.
If you want to try to proceed with repairs yourself, post back and we'll provide a link or two with tips on how to open up the Time Capsule and take out the insides.
Frankly, most users would probably be better off in this type of situation if they can decide to call it a day with the Time Capsule and go for either a replacement Time Capsule or another hard drive for backups.