Q: Help authorising ipod with new laptop

I recently got a new laptop as my old one broke. I downloaded itunes and copied my music into it. When I try to sync my ipod, a message appears saying 'this computer is no lnger authorised to play purhcased items on ipod..would you like to authorise (if not, 80 songs on ipod will be removed). I click 'authorise'  after which it asks for my username and password. Once I've put this in, it says successfully authorised but then asks me to authorsie again and continues along this cycle...