flashback issue

Hi,

Its a snapshot standby database . We dont maintain any flashback logs or archivelogs of this database. Suddenly I noticed this database is down .While starting it is showing below error. Can someone please guide how to open this database ... Found one document from oracle website . It is suggesing to drop the restore point. But while dropping it is showing
ORA-00933: SQL command not properly ended . Please help on this

SQL>  alter database flashback on;
alter database flashback on
*
ERROR at line 1:
ORA-38706: Cannot turn on FLASHBACK DATABASE logging.
ORA-38714: Instance recovery required.

SQL> select open_mode from v$database;