Logout user automatically when came in WordPress blog

I am using WordPress blog in a开发者_StackOverflow site. When user login and redirects in blog, they will be logged out automatically. How can I handle this?

If you are using wordpress framework for blog or make your website, than in that any other person shouldn't have permission to register on it, because if any other person will register than they can change content and data of your blog or website, and if you want to solve that problem than you have to add a side bar gadgets.