sql tuning issues

why is the following query not using indexes ? there are indexes on all the predicates and the stats are current , and i have deleted any  baselines and sql profiles

SELECT  DISTINCT a.acct_num
            FROM PATRON.ST_LEDGER_AVAIL_FUNDS a, ks_acct_ledger al, ks_ledger l
           WHERE     A.ACCT_NUM = l.acct_num
                 AND l.id = al.ledger_id
                 AND l.balance > 0
/

SQL> /

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Plan hash value: 3676943615

---------------------------------------------------------------------------------------------------------------------------------------------------------------
| Id  | Operation                      | Name                    | Rows  | Bytes |TempSpc| Cost (%CPU)| Time     | Pstart| Pstop |    TQ  |IN-OUT| PQ Distrib |
---------------------------------------------------------------------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT               |                         |   108K|  3277K|       |   633K  (3)| 02:06:41 |       |       |        |      |            |
|   1 |  PX COORDINATOR                |                         |       |       |       |            |          |       |       |        |      |            |
|   2 |   PX SEND QC (RANDOM)          | :TQ10004                |   108K|  3277K|       |   633K  (3)| 02:06:41 |       |       |  Q1,04 | P->S | QC (RAND)  |