kangoo warning light wont go out after starting?

about 6 weeks ago the engine managment light came on and after starting does not go out .have noticed blue smoke on starting and its getting harder to start
have changed the glow plugs and battery it started this morning after a few goes .some times it starts and it idels but you can not rev it you have to switch it of and back on again and its ok the warning light still comes back on and stays on after starting