If your Huawei modem is the B818 and the bottom light is blue that is normal.
I am assuming you posted from a Mobile Phone? If the mobile phone is on the Optus Network that rules out a Network Issue, if the Phone is on another network have a look at the link below for outages?
If you are new to the 4G Service have you logged into your Optus account to see if the service is active?
Do you have a device Laptop / Desktop Computer that you can connect via an ethernet cable to the Huawei Modem? If so try an ethernet connection.
If the service is not active or nothing else works and you can get to an Optus Store take the Hauwei modem one of your devices and see if they can get it working.