Computer Ports

As illustrated nicely in this Wikipedia entry (scroll down to "Types of Ports"), most computer ports and cables are identifiable as matching because they are the inverted match of one another.  Since, as described in the entry, the purpose of a port/cable is to make an interface connection between two devices, the port and cable need to be firmly connected, of matching type and in proper condition for a signal transfer to occur.  When verifying connections, first observe the cable and confirm that it should fit into the port.  Look over the cable and the port to make sure there is no obvious damage.  Then, check to make sure that the cable is firmly connected in the port.  If these three steps do not lead to a successful conclusion, you made need additional assistance. 
Computer Port