Time Capsule issue

Power off the Time Capsule, either by pulling the power cord from the back of the device, or pull the AC plug from the wall socket, whichever is easier for you.

Restart your Mac

Power up the Time Capsule again and let it run for a minute or two

Hold down the option key on your Mac while you click on the Time Machine "clock" icon at the top of the Mac's screen

Select Verify Backups and run the check

It may take anywhere from 5-30 minutes or more for the operation to complete, depending on how much data is stored on the Time Capsule hard drive. Let the process run until it completes.....or.....until you see an error message.

If an error message appears, post back with the exact text of the message.

You can watch the progress of the Verify Backups diagnostic check by clicking on the Time Machine "clock" icon at the top of the Mac's screen and then clicking on Open Time Machine Preferences.

Note.....the version of Time Capsule that you have is at least 9 years old and as much as 11+ depending on when the product was placed into service. The average useful life of this product was about 6-7 years, so you have had very good luck so far.

However, both the power supply and hard drive are frankly overdue to fail at this point, so you would not want to keep any data on the Time Capsule that you cannot afford to lose......unless you are running additional backups on another hard drive.