SQL> conn sys as sysdba
SQL> startup nomount
SQL> alter system set control_files=
'D:\ORACLE\ORADATA\ORA10\CONTROL02.CTL'
scope=spfile;
SQL> alter database mount
SQL> alter database open
SQL> startup nomount
SQL> alter system set control_files=
'D:\ORACLE\ORADATA\ORA10\CONTROL02.CTL'
scope=spfile;
SQL> alter database mount
SQL> alter database open