without ID vs with ID

You buy a ebook, you try to read it as soon as possible. Usually you skip bothering steps, like, register, open a "new" account, etc...

Sudenly you find a message that says you will be able to open this item only in this computer... you think "oh, yeah, yeah"

And you get your ebook, you start to read.. and you didn't realize is your dad's computer.

Happy for your purchase, you go to your computer, try to open your e-book, you instal the ADE, but you ID is not associated at your item!!!

WHAT CAN I DO?