Welcome to TPG Community, @daveburrows!
First, you have to make sure there's no issue with the power source. If other devices connected to that same source have no problem, then we can focus on the modem. You can also try plugging the modem to other power source. If same thing, you can perform a hard reset on the modem by pushing the RESET button at the back. Manual configuration may be required if modem does not connect back to the to internet automatically.
If all fails, you can send us a private message with your account details so we can check your options for replacement.
Cheers!
Aubrey
