Es57

I'm trying to open a .tga image file with Paint.NET. But instead of the actual image, I just get the grey-and-white transparency grid. I can see that the image seems to be somewhere behind, because when I use the color-selecting tool on it, I can have the various colors of the image in the color window, with a 0 alpha-transparency. Is there a way to disable this transparency so I can see the image and be able to modify it ? (I should mention that there is only on layer to that image.)