Try this procedure:
- Connect a phone to the first FXS port and pick up the handset
- Press the function button on the Cisco ATA (button on top surface)
- Press the digits 322873738 (FACTRESET) then press # on your telephone keypad
- Press * on your telephone keypad to confirm that you want to reset the Cisco ATA, then hang up the phone
If this procedure doesn't work, try to pass TFTP server with option 150 in your DHCP.
Now try to see if the ATA ask to TFTP for a configuration file.
If yes you must build a config file with no password.
You can find more info in attached document.
Regards.