Originally Posted by Erendralin
Usually the background,borders,buttons and almost every element of the modified UI looks like a grid with blue squares and white lines.
The grid means that the image files (.tga) are not being loaded in-game. Usually this problem happens when the image files are missing or in the wrong location. Since you're able to load the custom ui, the SkinDefinition file must be in the correct location. Another possibility is that the image files are corrupt or otherwise unreadable.
If you followed the directions from above from Brygard2007 something else must be the problem. I'm sorry but I don't know what to suggest.