Hello, I'm TV Tech1 and I'll be working with you to identify and help you resolve your problem. In your situation, it sounds like the TV's tuner isn't working correctly to scan and LOCK your TV channels into the tuner's memory.
However, before we call it bad, Samsung has a Plug and Play setting that resets the memory and builds a new list of available TV channels in your area. I think that Plug and Play setting is found in the Channels or the Setup Icon. They did make minor changes to the menu layout over the years, but that's the one setting you find in earlier versions of most TV sets. Later, I think they renamed the Plug and Play setting to either INTIALIZE or Factory Reset...and I believe that's found in an Icon called Support. I think they did that back in 2009 or 2010.
Check your menu, see if you can find that and reset your TV. Let it autoscan your channels, then we'll know if it just needed to be reset, or if the TV tuner is your problem.
Also, note that this setting ONLY appears if your TV is set to watch TV channels. If you are watching any other INPUT on your TV set, like HDMI or Video, or Component inputs (selected by the remote's SOURCE button) it actually turns off the Plug and Play or Initialize setting in the menu. It makes it gray out...or inaccessible.
This is the setup your TV model uses, it's shown in this picture --