Have you found any service info on ElectroTanya or the other manual/schematic sites?
I would start by looking for the power cabling between the power supply/backlight board and the Signal board and DVD player board. Often the proper voltage rails are marked on the connector. Typically you would have a 5VSB (standby-on all the time), +15, +5, and +3.3V, and perhaps a few others. See that they come up when power is applied. If not, look for shorted components on the affected rail, or an open/high ESR filter cap or a blown fuse.
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