Texture format (The Witcher)

I categorically welcome you, the problem with displaying textures, after editing. I chose the format DTX5 and many others, but the result is one - either first the texture is normal, and after the dialogue becomes black or transparent, or initially all translucent pixel, with left colors. I use Paint.net. Did anyone have such a problem and how did they solve it? And what format is right to save, normal textures do not have to see the full info.