Without further information, I will try to take a stab at the potential problem. When the set asks you to scan for channels, but you were already using it previously- you do not want to scan for channels.
Instead what has happened is that the TV's Source setting has changed (either inadvertently, or because the set lot communication with the cable/SAT box).
Please proceed by doing a full reboot as follows:
1) Shut the TV off and unplug the cable/SAT converter box from power.
2) Carefully remove and reconnect it's cable connecting it to the TV (HDMI, Scart, Component, etc.)- making sure it is connected securely on both ends.
3) Plug the cable/SAT box back in and give it a few minutes to reboot.
4) Turn the TV ON and use the Samsung's SOURCE button to toggle through the available Inputs to see which one restores your programming.
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