In order to get things working again, simply clear out your internet history, temporary internet files, cached files, and cookies and close down your browser.
You should find that when you reopen your browser everything is back to normal!
Unfortunately we can't provide detailed instructions for every browsers. However, you can usually find a setting to clear your cached files and cookies under the "File" menu, in a tab usually named something like "Tools", "Preferences" or "Settings". If you're unsure, most browsers have a comprehensive "Help" menu to assist you.