Help, I have not been able to use my ipod for 6 months now!!?

See I did not know you had to deauthorize the computer before sending it off to repair. So when I got it back after the repairs i was not able to play any of the songs that i purchased and those songs got deleted from my ipod. so when i get on itunes to play one of the songs i bought a dialog box appears to autorize computer so i enter my log in ID and pword and then it says successful 1 out 5 machines then i hit play to one of the songs i bought and the authorization dialog box appears again to authorize the computer? what do i do?