I would check your account with XLN. Go to 'My Account' 'My Products' for your serial number n the cakewalk site.
Hwever, sometimes a windows update can throw your authorisation. So you may have already done this. In which case, un-authrise the PC n the XLN site and re-Authorise.
When you are logged into XLN, your purchased kits are greyed out n the website.
Before you buy anything. check this thread. I'd recommend a Custom pack for best value
http://forum.cakewalk.com/FindPost/3739627