Apple iPhone 3G

Ok, here it is. Computer crashed.. Had to reinstall everything. When I sync the phone to iTunes it doesn't list the songs on my phone on the music list. I really can't get it to sync anymore. It says if I do a manual music sync I will erase everything on my phone and will be replaced by the stuff on my new music list in iTunes which is only the sample crap that downloaded from the windows sample music. Would love some help... Thanks