Need help. Internet Privacy

Hello. I am not a computer person and have no idea how all this stuff works, but somebody hacked my e-mail this winter and since that time, I keep recieving all sorts of dirty threatenings, and stuff. And As my password was changed I could not do anything, because I was a free Yahoo browser and could not remember the zip code number I entered when Opening up this accaunt. All right, the e-mail is gone, By time i got used to it, and was ok, but In some public forums, I read dirty stuff written from my name, with my pictures(not naked, just innocent pictures from yahoo family album). And the last drop was when in one of the porn sites I have seen my picture with an offer to have sex for 100 dollars. People, I do not havy any idea who is doing that. I have no idea what do they need from me, but they know how to track me. I mean, If i go to a new forum with a totally different screen name, they know about it at once-A new advertiement with dirty lie + my new screen name is shown out there for public. How do they do that? I have changed my screen name in all forums, went to a new one, THEY ARE CATCHING ME! How do they do that? And what should be the right reaction, because I am in panic. I do not want to show them that, and pretend to be calm and keep talking about funny stuff online, but Hey, What will I do if tomorrow they will post my address and phone number? Please, is there any way to secure myself and my web surfing? And how should I act? Should I leave the Net and get lost or just ignore them? pLEASEEEEE, HEEELPPPP