Welcome to the community!
Thanks for raising this to us, minjeong8342
For customers experiencing connection issues with their service, we recommend the best thing to do first is check if there's an outage.
If there are no known outages in your area, you can proceed with the troubleshooting steps indicated on this link:
If you are using a WIFI connection, then you may check these links to improve your home network.
If you need further assistance, please send us a private message with your TPG customer ID, username and complete address so we can take a look at your account.
To send a PM, please refer to this link: How do I private message (PM) in the community
I tried reset my modem but it wasn't work.
Also I checked nbn outage, and there is nothing wrong. Please check my file that I upload. Also there is light flashing with black modem-upstream and no light with ONLINE.