Welcome to Just Answer,
My name is John
It sound like you are having a failure of the 24v portion of your power supply, it supplies the backlight and some video function, it is a common failure and can cause no picture, dim picture and dead set.
Well then let see what i can do to help first off if you really want to try to order the part to fix it yourself (its $560) the module is the only part polariod sells to customers, it is the entire metal box inside but dont worry... i have some better news. It can be fixed for lots cheaper but you need a good bit of knowledge, i would recommend taking it too you local service center.
You will need all the 1000 microfarad capacitors replaced and check d9 and z4 this is what most ofter causes this failure. (a good shop it should cost less then $200.00) if you dont know of a good shop look on www.citysearch.com and if your in michigan come see me (but i bet your not close enough thats okay) this is a known issue and if you feel like tearing the power supply apart and fixing it you can give it a shot.
The caps will look swollen on top bulged while the others are flat. the diode is hide under the heat shink on the right hand side of the power input connector (if the connector was on in the position of being the lowest part (bottom of the board perception make this tricky)
May look like this:
Hope this helps,
If you have any questions let me know.
You can get the diode it is a standard power supply diode 1/4 watt and the caps from digikey.com