Q: Time Machine nor Backing Up Since Sierra Installed

Sierra is having issues and you should never use Time Machine over the top of an existing backup anyway.

The steps are to.

1. Archive the current backups.

Plug in a USB drive equal to drive size of the TC (You are mixing up the terms Time Machine.. software to do backup on the computer.. and Time Capsule.. hardware target for backups inside a router).

Archive is on the disk tab of the airport utility.

2. Once the backup finishes. it can take a day or so for 2TB disk that is full.

Erase the TC disk.. a quick erase is fine.

It only takes a couple of min.

3. Factory reset the TC and reconfigure it from airport utility under Sierra on one of your Macs.

Reset the preferences in Time Machine and it should start and run just fine.

But also you should read some of the other threads here about the problem.

For example.. preparing is expected to go a very long time when you are trying to use existing backup.. over wireless with both computers doing it together .. that will take days to complete.

Open the activity monitor and check that other processes are not using all the CPU time. One person discovered photos was chewing 90% of the processor doing some function that is part of the update and allowing no time for the TM backup to progress.

I had the same issue, eventually resolved by un installing Sophos Anti viorus

I Had same problem, the disk is not mounted automatically anymore you have to connect it mannually from finder. I spend many minutes talking with apple care, they were wondering why the capsule is not connecting automatically. Finally someone callled the engineering dept. For security reasons Sierra is not allowing automatic connection with external hard drives.