The POV-Ray docs can help you out here. Go read them. Have you applied textures to your objects. If you haven't, you might find that your ray tracer defaults your object to be black. This isn't as silly as it sounds.
Most ray tracers have several options for output file formats.
If you haven't explicitly specified the output format, there's a good chance it's not what you want it to be. This is a common mistake with POV-Ray 2.2 for UNIX which uses an obscure output format by default. Similarly, if you don't compile in the URT support for Rayshade, you will get MTV format output files. It's one of the very first freeware ray tracers, written by Mark Terrence vandeWettering, now with Pixar. Some image display programs use the file extension to determine the file contents, so if you call the file output.tga, and it's actually a PNG image, your display program may complain that the TGA file is corrupted.