please help retrieve lost songs in my iTunes library

Hello,

I've lost most of my music in my iTunes library and am hoping that someone can help me retrieve it. I was trying to add a second itunes account to my PC (windows 7), and in doing so I lost a lot of my music in my original iTunes account. The second library was never fully set up (which is not my concern right now), and has zero content in it. I am concerned about my missing music. How can I retrieve that? Thanks!