O.k then either the TV's own tuner went defective and that does happen or that cable although connected correctly may be dead , no signal in it , this could happen though a defective connector and very often where the cable system is split (cable splitters) in the house , if you don`t know where that splitter is then that would be the cable company that would need to check that .
Right now a way to find out who is the culprit would be to try another tv on this location or perhaps even bring in a cable box (if the other TV's have one ) and give it a try , that would also tell you if there I a signal on that cable.
Right now I`m not sure what you tried but you could also try this;
Unplug the TV's power cord and hold the power button directly on the tv ,keep holding it for 20 secs or so then let the tv sit unplugged for a couple of minutes before you try it again.
Again though , the quickest and most efficient way of testing that would be to try another tv there .
Either ways you`ll know if you need the cable company to repair the wiring or a new tv with a working tuner or may be even an external tuner or cable box connected to this one.
If that answers your questions for now please do not forget to rate or you can use the reply button before or after rating if you have other questions , thank you .