I agree with the battery as the first thing to try, especially if it is 5+ years old. Even if you try and jump it if dead you may not exceed the threshhold voltage for the car to crank. It could also be a bad ground, or loose cable at the ends which connect to ground and to the car but start with the simplest thing first and check the battery.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz