No video signal shows up when i turn on tv. i hear sound but get no visual. it worked last night. i didnt change/move anything. what could be wrong?

I had exact same problem with this TV. Went through the user manual. Page 32 shows how to reset this TV back to factory settings. I did that and the TV is working OK (knock on the wood). here are the steps for resetting it back to factory settings:

1. Go to menu
2. setup option
3. Highlight "installation" and hit enter
4. Open the "system status" and select "System information".
-- This will show you the model number, and the software version.
5. Use right arrow key to select "factory defaults".
6. Enter "0000" or your PIN and hit enter
7. TV will turn off after resetting.
8. Pull the power cord out of the outlet
9. Then plug the cord back and turn the TV ON.
10. Keep your fingers crossed and hopefully you will see the TV back to normal.

First, look at the screen in darkened room to see if you can see any slight glow from the screen, if it does, then the problem can be the T-CON (not getting the 12vdc) or the main logic board not feeding the signals to the T-CON board.
if not, next place to check will be the power supply module, make sure it has 24vdc which is required by the backlight inverter to work, the reason for not having 24vdc can be from bad DC filter caps (leaking/bulging top, high ESR) or short circuits in the inverter board which will cause the 24vdc supply to go into shutdown mode, so you may have to disconnect the power cable that feed the inverter board to see if the 24vdc will work without the inverter board hookup, you will need to apply about 3~4 amp of load to the 24vdc to make sure it can handle that. There are fuses on the backlight inverter boards also. So there is some troubleshooting you will have to do to find out the causes of the problem you are having.

If you are going to DIY and have proper tools, electronics knowledge, and know safety precaution then please read on:

Basic LCD monitor and TV troubleshooting guide:
http://www.fixya.com/support/r5093881-lcd_flat_panel_tv_troubleshooting_guide
http://www.fixya.com/support/r6150077-basic_lcd_monitors_troubleshooting
Failed TV and Monitors: http://s807.photobucket.com/albums/yy352/budm
Learn about bad caps: http://en.wikipedia.org/wiki/Capacitor_plague
Parts: www.shopjimmy.com
Capacitors kit: http://lcdalternatives.auctivacommerce.com/Default.aspx he can make you a set of caps.
Or www.digikey.com, just make sure to use caps with low ESR, 105c, high ripple current and long life rating such as PANASONIC FM or FC series.
Please post back what you find.