Bring the device back to its factory defaults:

This will clear the configs on the device and erase anything that was set on it. 

1. Plug in power adapter
2. Plug in a phone to ‘Phone 1′ port of the SPA-2102
3. Dial ****
4. You should hear ‘Configuration Option Menu’
5. Dial 73738#
   
6. Press 1 to confirm the reset