Black screen sound ok

I was watching tv tuesday night and I turned
the tv off to eat dinner. After eating I returned and
turned on the tv. The red light went out and the
green light came on, after a few seconds the sound
came on but the screen was completely black. I
tried everything but nothing i did worked.I suspect
that the power that going to the screen is not getting
there, I also suspect the problem is in the circuit board
that the power in jack is connected to. If this board has
to be replaced, what is the cost of this board?