My 2001 Mercedes c320 will not turn over to start even when I jump it.

This isn't an easy one to answer, because of the sophisticated "Drive Authorization System" (DAS) used on this car. One of the few things you can do, is try a second key. These keys do fail, giving symptoms much like yours. Hopefully you do have a second key, as no owner should have just one. If a second key doesn't work, it will need to be taken to a Mercedes specialist or dealer. They should be able to determine if the problem is the Ignition Switch (EIS), starter motor, or one of the many other components used for starting.

I have the same car. U can try clean the tip of your key. And replacing the battery in the key. And try a new battery. Get battery checked. If battery is no good it can mess up the codes in computer. Having computer codes reset will probably help also. My car is running fine now. I will say it good to check thesea small things 1st. And if they don't work. It's best to get a diagnostic did. Will save u a.lot of money. Theses cars can get expensive trying to figure it out