Lost SYS User Password

Make sure that the database and listener services are started. Then open a command prompt and log in as / as sysdba. Then change the sys password.
c:> sqlplus /nolog
SQL> connect / as sysdba
SQL> alter user sys identified by ,new password>;

If you get asked for a password when you log in as / you need to create or recreate the password file using orapw. Check the $ORACLE_HOME/database directory for a file called orapw<SID>. That is the password file for the database. Create (or recreate) it using:
c:\> orawpd file=$ORACLE_HOME/database/orapwd<SID> password=<password> entries=5