No, I don't think it has anything to do with codecs. You probably saved the PRV files the wrong way. Try doing this: 1. Get a picture of some unit 2. Open it in PhotoShop and select: Image>Canvas Size 3. Make sure that you have the same height and width (e.g. if it was 365X100, then make it 365X365) 4. Flip the image vertically 5. Hit Ctrl+Alt+I and change the image size to 64x64. 6. Save it as a *.tga 7. Rename the extension to *.prv. And you have a fully working PRV file.
You solution is very interesting. It is a process that I did not know. But the problem was easier than it seemed, and it has to do with what you proposed. In fact, it was all a problem with the screen resolution. I followed the suggestion of "Nigthgambler", who told me about that possibility. And he was right in full. The whole problem stemmed from the installation of a old game. I reconfigure the parameters of the screen and ... problem solved.