If you're original setup was done by professionals, it is more than likely that some form of encryption key has been used to ensure that bad people stay out of your network. If you can see or ping the pronto, your network settings (IP, etc) are correct. What has potentially changed is the encryption key used (or not used.....) to access the wireless network. If your BT device uses WEP, WPA or WPA2 to act as a security guard against illegal access to your network, then you would need to update the Pronto with the new key. The Pronto only supports WEP, not WPA or WPA2. Thus if your BT device does not support WEP, you would need to disable encyrption. Please note that this is not a recommended option (disabling encryption) as it does leave a rather important door open to hackers.

Also extenders tend not to like DHCP allocated IP addresses as they can change from one session to the next. I would usually create a DHCP reservation for the device based on its MAC address and ensure that the same IP is always allocated to that device on connect.