Hi thanks for your reply , when I took the battery out the key part of it also came apart don't know how , I was actually taking it apart to try the battery in another remote for my Merc so I could get to work!! When I got home I could not find the bit that clips on to keep the key blade secure, that's the bit with the transponder I think, I have looked high and low haven't yet found it!! So need new transponder and what not ?
Put the key in the ignition and turn it on so that the oignition is switched on. Then while the key is still in that position press the unlock and lock buttone, then immediately remove the key and try it. That should work the remote locking and unlocking.
But when you say it won't start, are you getting the "car with a key" symbol on the dash? if so are you 100% sure that you have the right key?
Removing the battery as you did will "lose" the remote locking and unlocking, but it should not affect the immobiliser.
Also check that you have put the battery in the right way round.