Well unfortunately it is impossible to know exactly what is wrong because this model has more shutdown circuits in it than any other I have ever seen. See all the circuits are monitored in this television and when one malfunctions it shuts down and gives us this symptom. I will give the most common causes and prices, hopefully that will assist you and if you need anything further after that please let me know and I will be happy to help.
The most common cause for this tv to shut down is the high voltage circuit, sometimes there are a few components that need to be replaced to get the set running again. If this circuit is the cause then you could be looking at somewhere between $300-$400 on average to have the set running again.
If the horizontal circuit is not the issue then most likely it is being caused by either the high voltage trippler or one of the picture tubes. If the trippler is the cause then you would be looking again at $300-$400 and if one of the picture tubes was the cause then you would be looking at around $600 (tubes are expensive and very hard to install.)
Lastly you could have a problem with the signal board, however this is rare. On your model the signal board could also run around $600. (also most of the time when a signal board fails it goes intermittently, some days the tv will work and then other days it will not)
I am sorry that I do not have any good new or quick fixes for your set. You definitely have a internal failure in your set. Please let me know if there is anything else I can do for you.
If you would like any additional information or have more questions please don't hesitate to ask!
Please never accept an answer until you are 100% satisfied and feel you can leave positive feedback. If I have answered your questions and met your needs then please press the green "accept" button. Otherwise please feel free to ask anything else to get your problem resolved. Positive feedback is always appreciated! Thank you,Tim Nolan