I have a LG 50 inch plasma and everytime I Turn it on ,it turns off within a couple seconds. What could be wrong with it

Your TV must be defect. And you need a tech on the TV to see what is wrong.
But my guess? it will be cheaper to buy a new one than have it repaired.

might have to change the bulb in the tv, should be in the back right corner should tell u something like a warning lable so u can find it,u will need a screw driver.

Hello
There is some over current consumption when the set heats up. Just see whether its cooling fans are working well. It can't be predicted the fault, as it need a through check up.

You probably have blown capacitors on the PSB-power supply board. Recaping with new UF caps works 90% of the time. The set turns itself of into a fault protection to keep from damaging more components internally. A few bucks a soldering iron some solder should do the trick.

Power supply board have dead capcitors.Know how to solders?These capacitors usally bulge or pop open,replaced these capacitors will solved this problem.Or tries websites Shopjimmy.com,Ebay.com to buy a Whole reburbish power supply board for the replacement.

My Lg was doing the same thing. Every movie we watched had subtitles running at the bottom of the screen. The button was at the bottom of the remote. Once we pressed it, it came up on the screen saying CC/OFF. Also had this happen on same TV with DVD player and had to turn it off with the DVD remote. Subtitles OFF/ON

Sure, you will need to replace the power supply circuit board asap. this will fix your issue.

Mainboard damaged and need to be replaced, try EBAY for a general picture of prices but you will need your product code wich is located in the back of the TV next to serial number.

probably you switch was sticking causing it to behave that way.just monitor you tv if it happen once more then it will be time to call the tech.standby my brother.