How can i prevent people from getting into my email account.?

I have changed my password but this person keeps getting into my email.How does he do it and how can i prevent it?

How can i prevent people from getting into my email account.?
If you aren't sharing your password with anyone (this includes having it written down somewhere), and if this person isn't guessing at your password because you use something so obvious, then I would say that you have a key logger installed on your PC. You need to get it uninstalled.
Reply:To change your secret question you have to email Yahoo Help and tell them what you want your new question/answer to be.
Reply:Try changing your security question to something else. Most likely they are able to access you email because they know the answer to your security question. IF that doesn't work, I would suggest starting a new account