see link:
https://community.oracle.com/thread/648581

-analyse als SYS user: 

select count(*) from dba_jobs_running;
select value from dba_scheduler_global_attribute where attribute_name='MAX_JOB_SLAVE_PROCESSES';
select value from v$parameter where name='sessions';
select count(*) from v$session ;
select * from sys.scheduler$_job;
select * from sys.scheduler$_window;
select logins from v$instance;
execute dbms_service.start_service;
select * from DBA_SCHEDULER_GLOBAL_ATTRIBUTE where attribute_name='CURRENT_OPEN_WINDOW';



exec dbms_scheduler.set_scheduler_attribute('SCHEDULER_DISABLED', 'TRUE');
alter system set job_queue_processes=0;
exec dbms_ijob.set_enabled(FALSE); 
alter system flush shared_pool;
exec dbms_ijob.set_enabled(TRUE);
alter system set job_queue_processes=99;
exec dbms_scheduler.set_scheduler_attribute('SCHEDULER_DISABLED', 'FALSE');