Your cache contains a history of all visited sites, images, audio files, etc. When returning to a site, files are retrieved from your cache instead of downloading again from the website. This is meant for faster internet browsing, but a very full browser cache can actually cause problems and may not reflect the current website.
If you can access an electronic resource in a private or protected browser window, and you cannot access the same resource in a regular browser window, then your browser cache may be interfering with access and need to be cleared.
The following links will provide step by step instructions on how to clear your cache.