scheduler - EPiServer schedule job not running automatically -

i working on episerver cms6. schedule jobs not running automatically. when tried run manually work properly. there configuration missing?

check database, in table tblscheduleditem. job "hangs" , prevents other jobs starting. "1" in column isrunning, , check if lastexec while ago. set isrunning 0. wait minute (or restart episerver scheduler service) , see if jobs start running again.