I think i am fraud of email account. someone used my email account to post some ad on the website. I have no idea the website.So i had to change my email account. I need to know if someone is hacking my email or computer.

Do not worry if someone is using you Email Account than IP Address of his Machine will be registered and whoever is doing the same will be caught once you make complaint in Cyber Police.
Whenever any email or any net account is opened on any conputer IP Address (Unique Internet Address) gets registered.
Don't worry.