Unless the browser has a problem interpreting the links, HTTP reponse 404 (Page not found) is a server side issue.
Some websites use JavaScript for links, as well as the inserting of emoticons in the text window here. If it is disabled, those functions will not work.
For Mozilla Firefox, click Edit -> Preferences -> Web Features -> Enable JavaScript.
For Internet Explorer, Tools -> Internet Options -> Security -> Custom Level. Scroll down to find the Scripting section. Enable Active Scripting, Allow Paste Operations Via Script and Scripting of Java Applets.
If you in IE has conciously set a higher security level, you can allow specific sites to bypass it by clicking on the "Trusted Sites" icon under the Security section in Internet Options, and pressing the "Sites..." button.
I am not a Windows expert, however, so other possibilities might be expressed by Kyo and others.
A favorite tip is always to use Windows Update.