Where do you have this case statemtent? Or, is it prehaps a case expression?
If you don't want some of the rows in you result, you typically "filter" them away using a WHERE clause, e.g.
SELECT * FROM sometable
WHERE NOT (a.GL_ACC < '4001' AND A.GL_ENT = '2000' AND b.GLRD_DESC = 'NS')
Or like this, easier to read:
SELECT * FROM tablea, tableb
WHERE a.GL_ACC >= '4001'
AND A.GL_ENT <> '2000'
AND b.GLRD_DESC <> 'NS'