There is usually a wall plate switch to power the antenna on for watching TV via the antenna and then off via able. When in the antenna mode, there is a green LED to indicate the antenna is on.
If you are using the antenna and suddenly lost all channels, I would check to see if the green LED is still on. If it is not, that is your problem and I would start checking fuses and power to it, etc.
When in the antenna mode, there is a green LED to indicate the antenna is on.
Just FYI - Some (mine included) don't have an LED, just the little push button, which is often obscured by coax connected to the fitting. Of course, the lack of the LED makes troubleshooting more difficult.
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Mine used to do that. I added a better TV antenna from Amazon mounted on a pole using a flag pole buddy on the rear ladder. The winegard omni POS is fine in town, but get a couple miles outside the city limits and it doesn't pick up squat.