Okay, along the way during the installation of 11g, you were prompted for a username for sys and system. If you don't remember what you did for that step (use one password for all, or went to password management and used separate/different passwords, you can change the password(s) at the command line.

sqlplus /nolog
conn / as sysdba
alter user identified by ;
repeat for the other account

After that, you will be able to logon to Database Control (the version of OEM you are using since it is single database).