I need some more information from you in order to help you out. Where are you pre-ordering Black Ops 2? GameStop?
I'm sure you entered your yahoo mail correctly, but double check. Also make sure your yahoo mail hasn't been deactivated, since Yahoo does deactivate email accounts for inactivity. Lastly if all fails, a simple solution would be to create a gmail account that forwards mail to your yahoo account and then use that gmail email address for pre-ordering Black Ops 2. All important emails regarding your Black Ops 2 preorder will be forwarded to your yahoo account.