|Have you tried it using other browsers? |
When you checked the link, did you try using the "view image" so that it opens alone in the browser?
If the links are valid, then it may be not having images enabled in the browser (check to see if images are enabled), the browser cache is full (try clearing the cache), the dns resolver may be thrashed (try flushing the dns cache), or perhaps your host has disallowed images for whatever reason (contact support).
You might also try uploading one or more images to an image hosting site, update the links on your page, and see if they'll display that way. If they do, then it's *probably* something that your host is doing.