Shortly after turning on my 2007 samsung 42" LCD TV, the sound turns off.

Barrie, what do you mean bye bleep? And what kind of tv and what kind of service( directv/cable)?

Its not your tv that is the problem unless it is shutting off altogether. If your tv is turning off then check out the ballast assembly. If it's just the signal going in and out from your directv, then sorry but that's your box that is the issue not the service itself. Check out what model of box you have and they are known for blowing capacitors. If you are in contract still then complain to directv. If not then I suggest finding a used one or open up your box and see if your capacitors are blown. If you don't know what those are here is a good basic video:

http://www.youtube.com/watch?v=YCSNWi3UHf4

I have comcast and get buzzing from the box when everything is off. Do you have the option of unplugging it and having the t.v. on by itself or will the provider have to come reprogram it. If not, disconnect box to rule out t.v. before t.v. warranty is out.

If this is a DirecTV receiver, you should be contacting DirecTV as support is included as part of your contract. If you do not have a DirecTV contract, I don't think your receiver is every going to work.

the directv needs hookedup to the tv, also the dvd player needs hooked up to the back of the tv, what type of cabling are you using, red/white/yellow or coax (where it screws in) or does it plug in and say hdmi, etc.

When the TV is on, need to check the back light is on(go back side & look into through)

If the back light is on -- need to exchange the Main Board
no back light -- exchange the Power Board --- 95%
exchange the LCD panel --- 5%(inverter)

My tv is still under warranty so I called Samsung and they're sending someone out to look at it.
Thanks!

Your DirecTV signal is probably too low. That would produce the small black rectangles (pixilation). Also, try replacing the cable you are using to get the signal from the DirecTV receiver.

This could be 1 of three things! 1-main lcd panel
2-y sustain module
3-z sustain module

This is something you cannot do yourself my friend.

This is likely due to heat expansion (turned on) and contraction (turned off).