I have a plasma lg 42px4dv-aa tv which wont turn on i press the stand by button snd no green o red light come on

SOURCE: Lg tv will not turn on, red light

i think your bulb is shot must be replaced

SOURCE: LG 42 plasma power problem

needs power supply Part number 6709900023A
it is a 171 dollar part, you should be able to order through LG,

SOURCE: LG 50px4dr plasma tv turns off immediately after

The problem could come from the power supply at the first suspected one. If you have a knowledge of trouble shooting, open the cover then examine if any caps there look poping up. Use your finger touch on the top of caps you will feel it. If not, check all the fuses there then disconnect all the cables from power sup to other boards, except the main board. Check Va and Vs according to the label attached on the back of panel. If the power sup shut down, replace it with a new one. Hope it helps.

SOURCE: I have an LG plasma TV, model: 50PC1DRA. We had a

Defective power board. Maybe best to call local service man.

SOURCE: 61" plasam TV will not turn on

This is one of two problems, Bad capacitors in the power supply or your Y Sustain board has failed, I would go for the first, take the back off your tv and look for swollen or domed shaped capacitors on the power supply, They may also leak a brown liquid like substance.
Replace all that you can see and this should cure the fault.