What if some one hacked in my email account?

Hi, I'm new at this site and I hope some of you can be patient with me.

*) Can any one advice if there is a way to find out if some one has hacked in to your yahoo email account and if so how can I find out?

2) I think I have know who hacked me but I can't confront them because I don't associated with them anymore and I don't live in that state.

*) I know this might be wrong to do but, this people are making my life hell and I want to know if I can find out anything based on their email (since I have it) to bring up to court for my protection.

Please advice,

Cristiano