Hello, Sorry you're having problems. What is the full model number off of the back of the TV please?
Also what is the rough age of the set?
Thank you for the reply.
Unfortunately that is all you can try on a user level, and this indicates the set has a fault either in the mainboard or the power supply board. There are no quick fixes for this and the set requires component level testing and replacement to fix it. The average cost for this repair on this set is in the $250-$300 range, and given the set can be replaced with a brand new 42" LED for the same cost- this is not a cost effective repair. I'm sorry for the bad news here and wish there were a quick fix.
Alternatively, if you're looking to attempt a DIY repair, then you will need a multi-meter (volt meter) and to be comfortable removing the back of the set to test live voltages. If that is something you're looking to do- let me know and we can proceed.
Other than that, I'm sorry for the bad news here and wish there were a quick fix.
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Do you need further assistance with this?