1. Shutdown database
2. Set following parameters in init.ora

for automatic archiving of redo logs,
path for the archive redo logs..
and format for the arch redo logs

log_archive_start = true
log_archive_dest = "location=D:\oracle\oradata\ORCL\arch"
log_archive_format = ARCH_T%TS%S.ARC

3. startup database and mount, don't OPEN
svrmgr>STARTUP MOUNT;
svrmgr>ALTER DATABASE ARCHIVELOG
svrmgr>ALTER DATABASE OPEN;

4.SELECT log_mode from v$database;

should show u ARCHOVELOG


HTH

Sameer