look

Code:
sys@DEV817>alter database datafile 'D:\ORACLE\ORADATA\DEV817\DATA_SMALL01.DBF' offline;

Database altered.

sys@DEV817>alter database datafile 'D:\ORACLE\ORADATA\DEV817\DATA_SMALL01.DBF' online;
alter database datafile 'D:\ORACLE\ORADATA\DEV817\DATA_SMALL01.DBF' online
*
ERROR at line 1:
ORA-01113: file 8 needs media recovery
ORA-01110: data file 8: 'D:\ORACLE\ORADATA\DEV817\DATA_SMALL01.DBF'


sys@DEV817>alter system switch logfile;

System altered.

sys@DEV817>r
  1* alter system switch logfile

System altered.

sys@DEV817>r
  1* alter system switch logfile

System altered.

sys@DEV817>r
  1* alter system switch logfile

System altered.

sys@DEV817>r
  1* alter system switch logfile

System altered.

sys@DEV817>r
  1* alter system switch logfile

System altered.

sys@DEV817>r
  1* alter system switch logfile

System altered.

sys@DEV817>r
  1* alter system switch logfile

System altered.

sys@DEV817>r
  1* alter system switch logfile

System altered.

sys@DEV817>shutdown abort
ORACLE instance shut down.
sys@DEV817>startup mount
ORACLE instance started.

Total System Global Area   41764892 bytes
Fixed Size                    75804 bytes
Variable Size              33419264 bytes
Database Buffers            8192000 bytes
Redo Buffers                  77824 bytes
Database mounted.
sys@DEV817>recover datafile 'D:\ORACLE\ORADATA\DEV817\DATA_SMALL01.DBF';
ORA-00279: change 1306769 generated at 05/07/2002 22:54:48 needed for thread 1
ORA-00289: suggestion : D:\ORACLE\ORADATA\DEV817\ARCHIVE\DEV817T001S02245.ARC
ORA-00280: change 1306769 for thread 1 is in sequence #2245


Specify log: {=suggested | filename | AUTO | CANCEL}

Log applied.
Media recovery complete.
sys@DEV817>alter database open;

Database altered.

sys@DEV817>select sysdate from dual;

SYSDATE
--------------------
2002-MAY-07 22:58:59

sys@DEV817>select tablespace_name, file_name, status from dba_data_files;

TABLESPACE_NAME                FILE_NAME                                          STATUS
------------------------------ -------------------------------------------------- ---------
DRSYS                          D:\ORACLE\ORADATA\DEV817\DR01.DBF                  AVAILABLE
INDX                           D:\ORACLE\ORADATA\DEV817\INDX01.DBF                AVAILABLE
TOOLS                          D:\ORACLE\ORADATA\DEV817\TOOLS01.DBF               AVAILABLE
TEMP                           D:\ORACLE\ORADATA\DEV817\TEMP01.DBF                AVAILABLE
USERS                          D:\ORACLE\ORADATA\DEV817\USERS01.DBF               AVAILABLE
RBS                            D:\ORACLE\ORADATA\DEV817\RBS01.DBF                 AVAILABLE
SYSTEM                         D:\ORACLE\ORADATA\DEV817\SYSTEM01.DBF              AVAILABLE
DATA_SMALL                     D:\ORACLE\ORADATA\DEV817\DATA_SMALL01.DBF          AVAILABLE

8 rows selected.
are you sure it is not your problem?