For some reason my Itunes library has changed and its now using music from my computer library instead of my own music library. I also accidentally logged out of itunes and I don't how to recover my account. I also now can't put music on my ipod!

I was going to put some music on my ipod, Itunes opened and it said it needed something about a library. I wasn't really paying attention so I just clicked in random places. Now when I go on to my Itunes my music library is the library from my computer which is not what I want. And I don't know where my music has gone. I also now cannot put new music on my Ipod which is what I wanted to do in the first place. Please help!