That can be the problem in the main logic board. You need to look at the sinal generated by the power switch to see if it is there. Also need to look at the power supply DC filter caps and check the voltages to make sure they are OK.
If you are going to DIY and have proper tools and know safety precaution then please read on:

Please see my basic troubleshooting guide here:
http://www.fixya.com/support/r5093881-lcd_flat_panel_tv_troubleshooting_guide

http://s807.photobucket.com/home/budm/allalbums

http://en.wikipedia.org/wiki/Capacitor_plague

Parts: www.shopjimmy.com