2000 Other Jaguar Models DIDN'T START

Electrical problem
2000 Other Jaguar Models 6 cyl Wheel Drive Type unknown Automatic 99900 miles

The car is an S-Type.

I went over to my cousins house only for less than 45 minutes or so. Then I started my car, and it wouldn't start! Tried a few times and gave up. Then we tried about a half hour later, and it still didn't start. So, I called AAA, and it wasn't the battery. So, the AAA guy said maybe it's the starter. So I called for a tow truck. It was put on the huge bed type tow truck, and we drove about 9 miles. When we got home, my dad started the car, and it started! Tow truck driver said that happens when you go over speed bumps and when the car goes up and down, and maybe it could start for about a week, then it might go out again. Mind you that he and the first AAA guy start the car themselves. My dad seems to think it's not the starter, because it started. And he thought maybe it was because I have a lot of keys and keychains that makes it a bit heavy, and since it's computerized, the ignition is sensitive. What else could it be? Thank you!