Hi.
It is not a lose wire. If problem was a lose wire or a bad solder joint it would have been sensible to vibration and the TV would have turned off when touched.
It is not a software problem either. The software cannot turn off the TV completely, at most the TV would freeze or go in standby.
If TV goes off completely, the problem is usually a defective PSU in rare situations a defective inverted can also give similar problems.
The problem is usually the PSU, A component (usually a capacitor starts failing) The other capacitors in PSU can compensate the work that is not being done by the defective part, and the PSU works for a while, until problem starts happening more often and TV does not turn on at all. In some case a defective inverter can do the same. In that case the inverter oscillator section is defective. The problem with the inverter is very uncommon.
Check the power supply. Sometimes it is possible to see at a glance a burnt spot or capacitors bulged on top. If there is nothing at a glance the PSU should be tested before replacing it.
PSU part number is PSCV121106B the PSU is not available anymore, the repair must be done replacing the parts on PSU. Below the repair kit with the components. For safety reasons the repair must be done by a trained person.
Here the repair kit:
Repair Kit PSU PSCV1211068Regards.
Ginko