Your problem is that your TV is probably done; the circuitry that manages the picture source has frozen. Before giving up, you can check the manual to see if there is any sort of "hard reset" button hidden somewhere, and you can try unplugging all cables (power, picture, cable, etc.) for a day to see if it will "unstick," and beyond that you can open it up and search for bad capacitors in the same fashion as the Samsung sticky-thread in this same forum.
But given that this model appears to be only a 720P plasma, anything beyond that and you're probably out the same time and money if you just replace it.
Abacus Model 2.5 | Quad-Row FX with 256 Cherry Red Slider Beads | Applewood Frame | Water Cooling by Brita Filtration