I just in staled Burning Crusade for wow and it wont let me become a blood elf why is that

After installing the Burning Crusade, your account also needs to be upgraded to make use of the new event. Go to the battl.net website, log in with your details, and find your World of Warcraft subscription. Here you will find an option to "Add Game". Simply put in the authentication key from your TBC CD, and your account will work.