i have an iPhone 4s and i'm having problems connecting it to my macbook. sometimes it won't connect at all or it will connect for a second then disconnect, and sometimes it will rapidly connect then disconnect a lot of times. the usb ports of my macbook do work because i had no problem connecting a flash drive. and i can connect the iPhone using the same cord to another computer without a problem, it just won't connect to my macbook. anyone know what could be wrong?