The screen gets black in some minutes of working, the sound continues

My LG LCD HD TV was doing the same thing. I would turn it on and within about 10 minutes the screen would go black.

After much research and troubleshooting I ended up having to send it out for servicing.

Before you do that, try these steps

1. Is your TV plugged in to a power strip, splitter, UPS or other power sharing device? If so, plug it directly in to a wall outlet. If the TV is getting low power it can cause issues
2. Does your TV have other video sources plugged in to it? (Example, Digital Cable, DVD Player,XBox 360) If so, try a different source and see if the problem still happens. If the problem does away, it could be the source. If the problem still happens then its still a problem :-)