Permissions error github (ssh key not recognized)

I seem to have lost my permissions to a github account after pushing to it from another (local) repository. I am now receiving the following error:

git push 
Permission denied (publickey).fatal: 
The remote end hung up unexpectedly

I then took the following steps to regenerate a key:

ssh-keygen
Set up an ssh on my account for this laptop, using id_rsa.pub

However, this was unsuccessful. When I try the following code suggested, I receive the following error:

ssh-add -l
Could not open a connection to your authentication agent.

Any thoughts?