With a little knowledge in electronics and a multimeter, you can easily check out the power supply. Using the meter, verify that all the required voltages are present. See post #7 at:
http://www.avsforum.com/avs-vb/showt...ighlight=power
The voltage outputs are where the connectors attach and their levels should be silk screened on the circuit board.
I recently repaired 3 TVs, which in every case was a blown fuse in one the the low voltage circuits (50 cent item).
Since you did not mention otherwise, the above assumes you have no picture and audio.
If you have audio , but no picture.....more likely an issue with the 18 volt section of the power supply or the inverter board.