As was announced some 17 months ago, MobileMe closed on 1 July. You will not be able to log into it under any circumstances. If you did not migrate your account to iCloud before 1 August then the entire contents of your account have been deleted.
You can use your MobileMe email address and password to open an iCloud account - simply sign in at System Preferences>iCloud and enable Mail and any other data types you want to sync. This should reactivate the email address, though you will not be able to retrieve its previous contents.