If you have forgotten the username of your Gmail account, you can try out the following steps to recover it:
2.Click "I cannot access my account", below the Sign in button, and select "I've forgotten my username".
3.Enter your secondary email address (the email address you provided when you signed up for Gmail) in the "Email" field.
5.Enter the characters you see in the picture and click "Submit".
6.Check your secondary email account for a list of Gmail/Google Talk usernames associated with your secondary email address.
If you have forgotten the password for your Gmail account, you can refer to the following webpage to recover it:
Following link is of a third-party website. We recommend you to update your security software before clicking on the link.
Hope this will help you.