The only way that you might be able to access the data on the 3 TB hard drive inside the Time Capsule is to physically open up the Time Capsule and remove the hard drive. Then, the hard drive can be placed in an enclosure or caddy to see if the hard drive might still be operational. If it is, then the data on the 3 TB drive can be copied over to another USB drive which you can use in case you need the data on the Time Capsule hard drive.
This is a job for a professional who is experienced with operations like this. This is not a job for normal users or even do-it-yourself type folks.
That is why I suggested that you take the Time Capsule to a Data Restoration Specialist. Unfortunately, this type of service is very expensive.
If the Data Restoration Specialist finds that the hard drive is still operating correctly, then you know that something else inside the Time Capsule has failed........likely a power supply. Apple will not offer repairs or parts for the Time Capsule, but an independent repair shop might be able to help if they can find spare parts from other Time Capsules. If they can, then you could have them reinstall the hard drive and you could continue to use the Time Capsule just like you did before.
But again, these types repairs are also expensive, and if the Time Capsule is 5+ years old, other internal parts are subject to failure. If it were me, I would not attempt to repair the Time Capsule, but it will be up to you to decide how you want to proceed.
If the Time Capsule hard drive is defective, about the only thing you can do is crush the hard drive to destroy it.