Never having used blogger, don't know if this will be of help!
if I'm reading your post correctly you have Google Blogger that uses your Yahoo address.
You also have a gmail/google account.
You have a password for your Blogger - lets call that password 1. I'm assuming that you have a username for the Blogger, which may even be your yahoo email address.
Your yahoo address will also have a password - lets call it password 2
You also have a password for your gmail/google account - password 3
Go to the google home page. Look in the top right corner of the page. Does it say you are signed in? If so, sign out. It might be that you are not fully signed out of Blogger when trying to use your gmail/google account details.
Now try to log in to your Blogger. Use the username for it and its password is the one we're caliing password 1.
If you get in to it, then sign out and make sure it says you have signed out on the google home page.
Now try to sign in on the google home page using the gmail/google account details which will include password 3
If you get in, then remember to fully sign out.
Try using a different browser and see what happens.
One other thing you could try is change the email address linked to Blogger to your google one.