On Step 3, I clicked Purchase & Print and it just keeps spinning (is stuck).  What can I do?

It should only take a few seconds to create a label once you click Purchase & Print. When you click Purchase & Print, the information is sent to USPS and they are returning a label; this can take several seconds. If it takes longer than 10 seconds something probably went wrong. Usually, this is due to some sort of browser issue.  If this happens and you get 'stuck' it's best to bail out. Before attempting to do another label, you'll want to clear your cookies, temporary files, etc. After you've done this, close the browser and try again with a fresh browser. 

See the article titled ´╗┐Clearing Browser Data and Cookies for instructions on how to clear your cookies on the most popular browsers.