The TV powers on and even displays the brand logo when turning on. After that, there is no display on the TV but sound. I can see moving images in the back. How can I fix this?

Do a reset to this TV, and then check. There are two methods to reset TVs. The first is simple to do; a Hard Reset. The other is somewhat skilled; is a Factory Reset (System Reset). To make it a hard reset, just unplug the TV from AC mains wall socket, and re-plug it back after 15 minutes or so. If you do this by overnight is better. This procedure will make it a hard reset. If you want to make it a system reset [Factory Reset]; you have to enter its service mode option, and select the factory reset option. If you wish to get some details; check the site linked here. Pull up older posts.
http://electronicshelponline.blogspot.com/
Service mode entry, adjust and exit procedure to many popular brand TVs are given. Never forget to exit the service mode, after all adjustments have been done.
If it do not help, check and replace the main digital board. It is faulty.

Do a hard reset to this set, and check. There are two methods to reset TVs. The first is simple to do; a Hard Reset. The other is somewhat skilled; is a Factory Reset (System Reset). To make it a hard reset, just unplug the TV from AC mains wall socket, and re-plug it back after 15 minutes or so. If you do this by overnight is better. This procedure will make it a hard reset. If you want to make it a system reset [Factory Reset]; you have to enter its service mode option, and select the factory reset option. If you wish to get some details; check the site linked here. Pull up older posts. http://electronicshelponline.blogspot.com/
Service mode entry, adjust and exit procedure to many popular brand TVs are given. Never forget to exit the service mode, after all adjustments have been done.

inverter board may be used to power backlight for the lcd display. If it is similar to laptop lcd displays in functionality .
http://www.ehow.com/how_7501465_check-tv-inverter-board.html

If your screen is black but an image can be seen against bright light then your backlight / inverter is bad and needs to be replaced.

I would suspect the main board as well

The inverter may have gone out. If the display is momentary such as for the logo, the inverter cannot hold the high voltage to sustain for the back-light. Shine a flash light on the screen and see if you can detect any images. If you can, then the back-light inverter is bad.

will not turn off power with out unplugin it

Hello,
Please call me 323-767-6030 and I will go through with you.

Does the lcd screen have a glow to it ? Or is it really dim if u get real close to screen u can see images moving ?
it it has a glow to it you panel lighting is fine but you control board is bad. If you have a dark screen and see faint images you panel back lighting is out u can check the power with a meter at the connection to inverter board on panel.