Over time, ports on your electronic equipment can become clogged with dust and other debris. And if you're having trouble getting USB or other devices to work with your computer, cleaning any grime from the connecting ports is a good first step.
Turn off the hardware first. If you can see that the port is severely clogged--say, with peanut butter or another thick, child-friendly substance--gently dig the gunk out with toothpicks. But remember: Ethernet, serial, and other jacks rely on fragile pins, so try to move in and out on the same path instead of swirling around the sides.
For less sticky situations, use a can of compressed air (actually pressurized gases) to blast out loose bits. These cans sell for $5 to $10 at any computer store. (Keep them away from children: The gases are dangerous to inhale and come out extremely cold.) Fire at the target in short bursts.
Finish cleaning with a cotton swab dipped in rubbing alcohol or electronics cleaner. Leave the device turned off for a couple hours to dry.