I have a 2003 Jaguar x-type.  It has just over 100,000 miles on it.  It has currently be at the dealer for 3 weeks because the security system is telling the engine that it is being stolen.  The dealer said it was the ignition barrel switch security transceiver.  We found the part in the UK.  They put it on my car and it did not work.  Any ideas on how we an get my car started again

first --will it turn over on the key and wont fire--or is there no response from the key at all-==lights etc  ???? ---

have you tried disconnecting the  battery completely for a while ???? then reconnecting with a fully charged battery  ????

if I had this problem with my car ?  I would phone an auto electrician and explain the situation to them, and also ask them if they can find out the problem or not !  the problem with our cars is the ECU (electronic control unit )  which controls ignition , fuel system, anti locking brakes, etc. hope this helps ?  all the best dave.