Hei,
It seems that your instance crashed, and your lost redo log is needed by instance recovery.
In such case, the only solution is restore backup(no matter hot or cold) and do incomplete recovery.
If you really have no any backup, the only final solution is use undocumented parameter:
_allow_resetlogs_corruption= true.
and startup mount database,
Recover database until cancel
Cancel
Alter database open resetlogs.
Do full exp and rebuild your database.
Good luck.