Lost my itunes

Hello,

I had a virus and had to reformat the computer. I thoght that once created the itune is a self supported and existing program that wouldn,t be affected by my problems and once computer on i wil register back and that,s it. Just found out that i was wrong. Lost everything. I loged into itunes but it is obvious by now that it has different library and features. Where is my old one? Can i recover it? Once i sign in and want to download stuff it warns me that the iphone has a different library. Can i go back to my initial ittunes?
If anyone can help will be much appreciated.
Thank you