You can check if there's an NBN outage in your area. If none, try restarting your modem and nbn box (if you have one). Reseat the cables, make sure they are securely connected. Check the light indicators on your modem, if you have the DSL/WAN light on but no Internet light, manual configuration may be required.
If you have tried all these steps and connection remains offline, send us a private message with your TPG account details and let's have a closer look.