Reset the TC to factory.. redo the setup from Yosemite version Airport Utility.. no files are lost doing this.
Factory reset universal
Power off the TC.. ie pull the power cord or power off at the wall.. wait 10sec.. hold in the reset button.. be gentle.. power on again still holding in reset.. and keep holding it in for another 10sec. You may need some help as it is hard to both hold in reset and apply power. It will show success by rapidly blinking the front led. Release the reset.. and wait a couple of min for the TC to reset and come back with factory settings. If the front LED doesn’t blink rapidly you missed it and simply try again. The reset is fairly fragile in these.. press it so you feel it just click and no more.. I have seen people bend the lever or even break it. I use a toothpick as tool.
N.B. None of your files on the hard disk of the TC are deleted.. this simply clears out the router settings of the TC.
When you do the setup, give the TC short names with no spaces and pure alphanumeric characters.. same for passwords.. 8-20 characters.
Now in Finder mount the TC by IP address rather than by name.
Use Go, Connect to Server from top menu,
SMB://10.0.1.1 for example.
It has to be static IP which is default in router mode but not so in bridge.
If you are bridged use the name or fix the IP.. dhcp reservation in the main router.
Type in like this for name.
SMB://TCname.local (replace with your new name and local is default domain .. it is important and helps).
Remember to save the password in the keychain when asked.
Good luck.. and if it fails clean install Mavericks or even Mountain Lion.. they work so much better.
