If you have checked the links and they appear to be correct then the suggestion I can give you is to make sure the CSS file is uploaded to the server (and at the correct location relative to the root). Sometimes what happens is that the HTML page is uploaded but people forget to upload the other files like images and CSS files. This creates a problem.
If this is not the case for you then please post a link here so that people can have a quick look at it.
Good luck.