When you set up your Yahoo account, did you supply an alternate email address to have info sent to in a case like this...?
Someone tried to hack into my hotmail account and after a number of tries, hotmail locked the account and I could not log in using my password. When I tried to log in, I got a message from Microsoft saying to go to my alternate account and retrieve a code that was sent to that email and enter that code into the message Microsoft had sent.. I followed the instructions and was then able to access my hotmail account. I immediately set up a new password which was longer and included caps and numbers. It has been fine since.

ALSO, when you set up an email account with hotmail, or yahoo or whatever... make sure you make note of whatever info you supplied to set up the account. When I set up my accounts, I did NOT use my actual birthday or other personal information. SO, after a couple of years when asked to supply the info that was used to set up the account, I was lucky that I had kept a record of such.

This probably won't help with your current problem, but may help with a similar problem in the future.