I have Windows XP (SP3) and iTunes is freezing when the authorization box appears. What can I do to get iTunes to unfreeze and make a purchase?

This problem has been occuring intermittently over the last few months and I thought it was resolved with an iTunes update. It later reappeared so I updated to the latest software and still no go. Itunes will also freeze if I pull up the "de-authorize this computer" option. I am not a computer whiz so any suggestions have to be in layman's terms. Thank you for your help. I'd like to be able to update my apps via computer and also make new purchases.