This is all going to boil down to how many username accounts you have and exactly which one registered which blog. There is only one means of account recovery so please read on.
You must be logged in as Admin http://en.support.wordpress.com/user-roles/#administrator under the exact same username account that registered the blog to access the blog's dashboard.
Clicking this link should display all your blogs registered under the same username, including the hidden ones: https://dashboard.wordpress.com/wp-admin/index.php?page=my-blogs&show=hidden
If you do not see the blog here http://en.support.wordpress.com/my-blogs/ then
follow this guide > http://en.support.wordpress.com/my-blogs/#my-blogs-dashboard-visibility
If you have lost your log-in information you can visit https://en.wordpress.com/wp-login.php?action=lostpassword
If required please complete the form for account recovery at this link https://en.wordpress.com/wp-login.php?action=recovery and submit it to the Account Recovery Staff so they can contact you by email ie. not on these public support forums which are available to everyone with internet access.