I would tend to suspect the power supply.
If there is no standby light then the standby PSU (if it has one) is likely yo be the culprit.
Depending on how seriously the manufacturer wants to reduce the power consumption in standby, the device may either keep the main PSU active, or disable it in standby and have another low power PSU drive the standby circuitry.
Failure of the standby PSU may make it impossible to enable the main PSU. If there is no standby PSU then failure of the main PSU is more likely.
I have no idea what the Sony Bravia LCD TV that you have has as a PSU.