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You said you come upto the login screen (I assume it is Windows 7 login screen). Then it is not a BIOS related error and does not need the removal of BIOS battery.
Usually when you do the factory reset, you will come to a step where it will ask you for a username and password to be entered so that next time onwards you can use that username/password combination for logging. See the below tutorial from step 10 onwards. Clean Install - Windows 7
Did you come accross this step? Do you remember what you have entered here?
If you still face problems in logging on, I suggest you to read the above tutorial carefully from step 10 onwards and do the factory reset again. In your case you will not be asked for the steps 13, 14, 19 and 21 in the tutorial during factory reset.