Why isnt my phone working????

i have a samsung sch-u520 i recently got a usb cord for it so i could put music and ringtones and stuff on it i installed the phone to my computer but when i plug my phone in nothing pops up i look under computer and it says theres nothing in the usb port but it makes the noise when i plug it in whats going on? why isnt it working? how do u make it work?