Oracle Query is returning value when setting value to it, but not returning value when passing date value

Oracle Query is returning value when setting value to it, but not
returning value when passing date value

My below query is not returning any values when i pass the START_DATE and
END_DATE as parameter to my oracle procedure. But when i set actual date
in the query i am getting results. Kindly help me what is the mistake i
have done here. Thanks in advance.
SELECT INCIDENT_ID
FROM INC_SM1 I
WHERE
I.CLOSE_TIME >= TO_DATE(START_DATE,'DD-MON-YYYY HH24:MI:SS')
AND I.CLOSE_TIME < TO_DATE(END_DATE,'DD-MON-YYYY HH24:MI:SS')
The below query is returning values, when I run my procedure
SELECT INCIDENT_ID
FROM INC_SM1 I
WHERE
I.CLOSE_TIME >= TO_DATE('01-JUL-2013 00:00','DD-MON-YYYY HH24:MI')
AND I.CLOSE_TIME < TO_DATE('01-AUG-2013 00:00','DD-MON-YYYY HH24:MI')
Note: My input to procedure is TO_DATE('01-JUL-2013 00:00','DD-MON-YYYY
HH24:MI')