Thank you for posting your question on Just Answer! I will be happy to help you with this problem. Can you please give us some more information so I can better answer your questions.
-Once on, you have no problems at all?
-How old is the unit?
Please give me this information and I will be happy to assist you further.
This is a very common problem with your tv, what has most likely happened (about 90% of the time) is the power supply has failed, more specifically there are a few caps in the power supply that have most likely failed. The unit will require component replacement to get it working again. Do you have any electronic repair experience, test equipment, and soldering equipment? If so I can assist you with this repair. If you do not have the above equipment and skills a repairman will be required for this repair, you can expect the bill to be around $200.
I am sorry that I don't have a magic button or a quick fix for you on this one, but component replacement will be required.
Please never accept an answer until you are 100% satisfied and feel you can leave positive feedback. If you would like any additional information or have more questions please don't hesitate to ask!
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