unable to insert row at id, but row does not exist

Here is the weird problem i am facing. I am trying to enter data using following query

insert into product_product 
(id, product_tmpl_id, make_equip, model_equip, name_template, serial_num_equip, location_equip, issue_date_equip, issue_to_equip, remarks_equip, pr, ch,  categ_id,valuation) 
values (700,700,'Nikon','Action 10x50 Lookout','Nikon Action 10x50 Lookout','671386','40 Wall St.','5/13/2004 12:00:00 AM','','OM''s OFFICE',62,72,502,'manual periodic');

I get the error :

ERROR:  duplicate key value violates unique constraint "product_product_pkey"
DETAIL:  Key (id)=(700) already exists.

********** Error **********

ERROR: duplicate key value violates unique constraint "product_product_pkey"
SQL state: 23505
Detail: Key (id)=(700) already exists.

I ran select query on that record like this:

select * from product_product
where id=700

It returns columns with no data(data includes id too)

I tried to run update query like this:

update product_product set 
                        product_tmpl_id=700,
                        make_equip='Nikon', 
                        model_equip='Action 10x50 Lookout', 
                        name_template='Nikon Action 10x50 Lookout', 
                        serial_num_equip='671386', 
                        location_equip='40 Wall St.', 
                        issue_date_equip='5/13/2004 12:00:00 AM', 
                        issue_to_equip='',
                        remarks_equip='OM''s OFFICE', 
                        pr=62, 
                        ch=72, 
                        categ_id=502,valuation='manual periodic' where id=700;

result was:

Query returned successfully: 0 rows affected, 1 ms execution time.

i tried delete query too but same output.

Also show all data shows nothing like id 700.

I don't know why this is happening.

I re indexed and Vacuumed my table from maintenance but same result.

Plz let me know what is wrong with it.

Thanks