Samsung LCD flat screen goes black. Turn tv off and back on it's fine for about 15 minutes and keeps doing it.

Just do a hard reset to this set and check. Unplug the TV from AC mains wall socket, and re-plug it back after 10 minutes or so. This must make it a hard reset.

Sounds like you either have a faulty LCD panel tab, failed LCD driver board, LCD/t-con panel bad connection, or a bad t-con. You will need to get a diagnoses to be sure.

This tv the LCD inverter board is dead,that why is not sustanning backlight for the LCD screen light to have the picture.Call Polaroid for warrenty repair,this tv under a year old.

Call LG for warrenty service,the tv Tuner board have problems.Must be replaced to solved this problems.

I have sound but my tv screen is black. Sometimes when I turn on the tv I get a picture but after 15 minutes or so the screen goes black again.
It's a 4 year old LCD.

There are two places to look for the problems, the backlight inverter board and the power supply. Look at the power supply first since it is easier to get to, look for burnt parts, bad capacitors, etc.
http://en.wikipedia.org/wiki/Capacitor_plague
Please post back what you find.

It can be the backlight inverter board is bad, or it can be as bad as the lamps also, also check power supply section for bad capacitors.
http://en.wikipedia.org/wiki/Capacitor_plague

check your LCD inverter maybe there is loss connection or some parts damage from inverter.

I had this problem on my 42" Philips. Just got it yesterday and worked fine on the tv stand. As soon as I mounted the TV to the wall via wall mount system, I had the exact same issue you did. Figured it out today.

The wall mount was putting pressure against the center of the back of the tv (tv set had a slightly rounded back plate, and the mount was a flat plate). As soon as I put spacers (part of the wall mount hardware set) between the wall mount braket and the tv so there was no contact except at the mounting holes, the tv worked fine.

My theory is the pressure pushed the tv back plate against some board components which caused them to overheat (no air flow); or put pressure on internal connectors. I dont know.

Hope this helps, may not apply to your situation.