We had this situation (all online redo logs in ACTIVE status) a few days ago. Regular scheduled hot backup was in progress and the 'begin backup' statements for some tablespaces hung. The database also appeared to be in hung status. We did a shutdown/restart. But trying to figure out what might have happened....Any inputs ??!!
Oracle was waiting for a checkpoint to complete. You were probably getting "checkpoint not complete" errors in your alert.log. If you frequently get this condition, you need to add more redo. Either bigger redo logs, more redo logs, or both.
The Database may be in Hot backup mode. check the tablespace status. Otherwise during hotbackup too much archivelog log been generated and that's why your archive log directroy may full. So now Oracle unable to archive online redolog. so your database is hang.