Trigger with Sequences number

Hi,
i converted SQL DBto Oracle by using SQL developer and Oralce created following sequences and trigger automatically see below. but when i trying to insert data into the table or use magrate data tool in sql developer, it gose to infinite loop and get error message as
ORA-06512: at "SYSMAN.HOOKUPPARTS_ID_TRG", line 15
ORA-04088: error during execution of trigger 'SYSMAN.HOOKUPPARTS_ID_TRG'
01013. 00000 -  "user requested cancel of current operation"
*Cause:    
*Action:

any help on this one will be much appreciated.

Thanks

Ying
CREATE SEQUENCE  HookupParts_Id_SEQ  
  MINVALUE 1 MAXVALUE 999999999999999999999999 INCREMENT BY 1  NOCYCLE ;

CREATE OR REPLACE TRIGGER HookupParts_Id_TRG BEFORE INSERT OR UPDATE ON HookupParts
FOR EACH ROW
DECLARE
v_newVal NUMBER(12) := 0;
v_incval NUMBER(12) := 0;
BEGIN
  IF INSERTING AND :new.Id IS NULL THEN
    SELECT  HookupParts_Id_SEQ.NEXTVAL INTO v_newVal FROM DUAL;
    -- If this is the first time this table have been inserted into (sequence == 1)
    IF v_newVal = 1 THEN
      --get the max indentity value from the table
      SELECT max(Id) INTO v_newVal FROM HookupParts;
      v_newVal := v_newVal + 1;
      --set the sequence to that value
      LOOP
           EXIT WHEN v_incval>=v_newVal;
           SELECT HookupParts_Id_SEQ.nextval INTO v_incval FROM dual;
      END LOOP;
    END IF;
    -- save this to emulate @@identity
   sqlserver_utilities.identity := v_newVal;
   -- assign the value from the sequence to emulate the identity column
   :new.Id := v_newVal;
  END IF;
END;