2005 Jaguar X-Type doesn't start

Test the battery for voltage it is holding and voltage under load. To do this, get a multi-meter and measure the voltage. It should be 12V. Then, try to start the car, if the voltage drops much at all, it will usually be a dramatic drop if battery is no good, the battery needs replacement.
Check the battery cables at the battery posts and at the starter solenoid, for the psoitive cable, and at the block, for the negative cable. Make sure they are tight and free of corrosion.
You may have a bad starter solenoid if the above tests and looks to be okay.
The starter may have to be removed to replace the solenoid.
If you have any further questions, come back to us anytime.