will not turn over

If you have a meter or testlight and want to check the basics, start by checking the starter, you should have battery voltage at the battery cable at the starter. You should have battery voltage (12.4 volts) at the START wire on the starter when your assistant turns the key to START. If this is all good, I'd suspect the starter. If it's not good, you have to dig deeper and trace power throught the START circuit. Otherwise, you need to tow the car to an auto electrical shop or a Jag specialist. Here's a directory link for you: https://repairpal.com/jaguar-repair-in-dayton-ohio