Verify the case of your file names, since you are most likely hosted on a Unix/Linux server where
Index.htm and index.htm are considered to be two different files, whereas under Windows they would
be one and the same. Also make sure that you have no spaces in folders or filenames.
Those things were all OK. I removed the theme and just used the
graphics, so it's working now. I also looked at the source code and
saw that it was still looking in the Images folder for pictures, so I
figured out that the FTP program, which I hadn't used before, wasn't
overwriting the files when I sent new versions. I deleted all the .htm
pages on the server, uploaded new ones, and it is all working now.
Thanks for the help.