Arduino loses usb connection
Your motor tries to draw to much current from the USB through the H-bridge. The USB can only provide 100 mA and your motor must be rated for more than that.

The safest option is to connect your H-bridge/motor from a separate power supply. As Wouter says, you should provide more information about your Arduino, the H-bridge and the motor you're trying to control, otherwise there's no way of telling what would work and what wouldn't.