I'm sorry to hear that you're having this issue.
Unfortunately, I'm not able to diagnose the unit, and I'm not sure what may have happened. If you haven't already, try registering your unit, which in some cases can extend your warranty by three months. You can do that here:
Then try to call 800-SAMSUNG, noted that you registered, and see if maybe they can assist further.
Suddenly after a year and a half the tv stopped working. When you turn it on there is just a black screen with small horizontal green bars on top and bottom corners, then it goes black, the tv turns off and on several times, then a high pitched sound comes on. Help!!