FTA channels? Like channel 9? This is provided via the aerial cable from your aerial. Perhaps check that is plugged in still. Then try the aerial in the tv plug and confirm the tv is getting /can scan FTA channels. After that use the fetch menu to rescan FTA channels (with the serial pledged in)
If the tv works but the fetch not then the fetch might be busted. Optus will swap it over for free on request.