To go over some of the basics,
1. Be sure that you have the cable company coaxial cable (the one with the threaded connector) screwed into the RF input on the back of the display.
2. Verify that when you do the channel scan, that you've selected cable rather than antenna.
3. Be sure that you're on the right input when trying to find the in the clear qam channels.
Also, are you finding any channels? even analog?
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