Very sorry to hear about your problem. First, let the system check itself out:http://support-us.samsung.com/cyber/popup/iframe/pop_troubleshooting_fr.jsp?idx=168711&modelname=UN55C7000WF&modelcode=&session_id=PtcvmjJlQ9xmkbhhmdLhL1yr2Jp7ynXsxlT3Z9GfxTRyrGYkH1mq%211358249754%21-1721297013%211336761570011
That often fixes many problems. However, if the problem continues, your TV requires service.
-- HD Tech
I get this note randomly on the TV. The TV is acting as a monitor and everything runs through my Denon 3312ci then out to the TV. I have a Samsung Blu-ray that was packaged with the TV when I bought it from Best Buy back in Decemeber 2010 and run Uverse for my tuner/cbl. All is connected vis HDMI cables and I have checked all of the cables and replaced them a couple of times. I have been into the Denon 3312ci programing for the upscaling and resolution from the source and found that for the TV (sat/cbl) source, where the "Check Signal Cable" cue comes up was selected as Analog and not Analog/HDMI
Samsung Tech support was not helpful with this.