Reauthorize?

I got Digital editions to read a book i bought of the internet, i authorized it without an ID. After some weeks i formatted my computer. I then downloaded the program again to continue on my book. Since it was authorized to the "old" digital editions (pre-formatted) i couldnt open my book. Now im in trouble because i authorized it without any ID, so how do i fix this so i can continue to read my book? do i just have to rebuy the book? Please help me, its for my exams