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If the TV appears to be stuck in Standby mode and will not turn on using either the remote control or the button on the TV itself, then it is likely that there is a fault on the power supply circuitry inside the TV.
There is a power supply board inside the TV that can be replaced if faulty.
If you are technically minded, you may want to obtain a replacement board and attempt to fit it yourself.
If you are not familiar with this type of repair, or you don't have the appropriate tools, then a local electronics or TV repair shop can carry out the repair for you.