We dont provide support for NON-TPG supplied modems, but i will try to help.
We recommend using a TPG supplied modem for the best support.
Most modems when trying to connect to the NBN get caught out with a VLAN setting.
If you can find where the VLAN settings are, you will need to choose VLAN ID 2.
You will also manually need to enter your TPG account USERNAME and PASSWORD.
You can check these credentials are valid by logging into the TPG account web page or web mail.