Unless there is a reason that you want to keep that private/public key pair (id_rsa/id_rsa.pub), or enjoy banging your head on the wall, I'd recommend just recreating them and updating your public key on github.
Start by making a backup copy of your ~/.ssh directory.
Enter the following and respond "y" to whether you want to over write the existing files.
ssh-keygen -t rsa
Copy the contents of the public key to your clipboard. (Below is how you should do it on a Mac).
cat ~/.ssh/id_rsa.pub | pbcopy
Go to your account on github and add this key.
Name: My new public key
Key: <PASTE>
Exit from your terminal and restart a new one.
If you get senseless error messages like "Enter your password" for your public key when you never entered one, consider this start over technique. As you see above, it's not complicated.