Time Capsule not working

Ref: If you can't back up or restore your Mac using Time Machine - Apple Support

General Troubleshooting Steps

1. Perform a "Factory Default" reset on the Time Capsule (TC).
   • A successful reset will result with a rapidly blinking LED status light.
   • Be aware that the reset button is quite fragile. Do not mash down on the button or it will be damaged, and would require opening up the base station and, potentially, voiding any existing warranty.
   • None of the files on the TC's internal hard drive will be erased with this type of reset.
2. Perform a "new" setup of the TC (again.)
   • Use the AirPort Utility on the computer that you will be using for Time Machine backups.
   • Use a short (16 characters or less) name for the base station name. Do not include spaces or special characters in that name. Ex: AEBS, TC, TCac, or TimeCapsule
   • Same as the base station name, use a short (16 characters or less) for the wireless network name. Again, do not use spaces or special characters in the name. (Optional) Use a different wireless network name each for the 2.4 & 5 GHz radios.
   • Use WPA2 Personal for the wireless security type.
   • Use wireless security passwords that are between 8-20 characters that consist of mixed case and numbers only. Do not use special characters, at least, not in the beginning to verify connectivity first. If successful, you can increase the security by adding special characters to the mix.
3. Enable IPv6 Link-local mode for the network interface on your computer that you will be using to connect to the TC.
   • System Preferences > Network > Ethernet OR Wi-Fi > Advanced > TCP/IP
   • Configure IPv6: Link-local only. Note: This would not apply if your ISP is providing you with a full implementation of IPv6, then just use the IPv6 setting that works for it as recommended by your ISP.