Why do I have to log in each time I contact a web site and why doesn't it last two weeks?

If I login to Yahoo, Microsoft, Facebook or whatever and l check it to last two weeks, why then does it require me to login again the next time I want to use the site. It only lasts the one session.

You should check to make sure your web browser isn't blocking the cookies sent from the sites. A cookie is a small packet of information sent from a site to your computer. They do all sorts of things, but the most common function is it stores your login information so it can automatically log you in each visit. If you post which browser you're using, and which operating system, I can walk you through checking to make sure your cookies are being stored properly.

this just happen I have no idea why