Why is my picture wider than the screen? It makes no difference what mode it is in. the picture is wider than the viewing width. Proscan 40" LCD

Check the viewing mode to be sure the screen is not in the stretch mode.

Back-light problem. Check and replace damaged component/s at its back-light inverter board, or replace this board as card basis. If you wish to get some details; check the site linked here. Surf the site with patience. Pull up older posts. It will be best to replace the inverter board as card basis.
http://electronicshelponline.blogspot.com/

the chroma ic could be shorting

you need to change the 'zoom' on the tv by the remote.
Normal mode frames the 4:3 video to the 16:9 picture area by displaying it in its original aspect ratio, with vertical gray or black bars on both sides of the screen. The disadvantage of this method is the fact that the image is small by virtue of not using the entire width of the screen. This is also known as the 4:3 mode.
Full mode Full mode horizontally stretches the 4:3 video evenly across the entire width of the screen. This is the proper mode to display anamorphic video. If used for standard aspect ratio video, everything on the screen will appear wider than normal. Contrast this with anamorphic video displayed without processing on a 4:3 display, in which people on the screen will appear taller than normal. This is also known as the 16:9 mode.
Zoom mode Zoom mode evenly stretches the picture both horizontally and vertically, until the picture fills the entire width of the screen. This crops out the top and bottom of the picture. This mode is used for letterboxed and open matte video.
14:9 mode Main article: 14:9
In 14:9 mode, the picture is magnified more than in Normal mode, but less than in Zoom mode, while retaining the original aspect ratio.
Wide Zoom mode Wide Zoom mode, also called Just mode, Horizon, or Smart Stretch, progressively stretches the picture horizontally, less in the middle and more on the edges. This allows normal aspect ratio video to be displayed across the entire width of the screen, with minimal cropping, and with much less of the unpleasing visual stretching effect of Full mode.

Under the settings, there's typically an option for the video width.
Under settings, go to Screen settings, then change the wide mode options to FULL.
This will make the picture fill the entire screen.
If that doesn't work, you may not be viewing an HD source. Change to an HD channel and you should have a full screen picture.

Check the resolution on your signal source. Well, first before doing that make sure the Proscan is on the right input i.e. make sure it is on the hdmi input if you have it and you signal source connected with an hdmi cable and then make sure the resolution on the signal source is 1080i fixed. Then there should be a button on the signal source remote (# hdzoom or format or aspect). You should be able to change the picture size with the #hdzoom, format , or aspect button.

The tv is most likely in a zoom mode, go to the menu screen and look for the picture options.

just look at the owners manual of how to adjust the picture

Check to see if you are on wide zoom mode in that input and check the definition. Go to your menu screen and check your video menu. There are different options for viewing. My inlaws prfer the words cut off it drives me crazy. Hope that helps

Depending on the application you are viewing the picture in you can shrink the application window. You could reduce the size of the viewable area but that defeats the purpose of the wide screen which is to provide a better viewing experience (to quote the marketing types). It sounds like....since the wider screen really has nothing to do with your picture size....you might want to adjust your picture size independent of screens and applications. There are a variety of free products out there that can do this...and some are really nifty...perhaps better than the software you might now be using.