All of a sudden TV will go to two stations only

Question

I have a Vizio 42L 42in LCD, it had been working fine until last night. While adjusting the picture size the TV all of a sudden went black. I am able to get the cable banner but no picture except on two channels. I have switched out my High Definition Cable Box with another one from another room to rule out the possibility that the cable box was not working but I still have the exact same problem. I have checked all of the controls and see nothing out of the usual. Any ideas?