Just a guess, it's probably Autoplay settings. I hate Autoplay. I'm sure there's a system setting to disable it, but I've always just disabled it for every drive using TweakUI. You can download it here:
If you are using a PC windows XP or higher this is what you do:
1- Go to "MY COMPUTER"
2- Go to the camera and scanner area. You should see your iPhone. It must be plugged into a USB port to see it.
3- Highlight (right click) on your iPhone in "My Computer"
4- Click Properties
5- Click "Events"
6- Under "Actions" check the box that says "Take no action"