If you have just plugged in a crappy patch cable, your Cisco switch my kill/disable or have errors on a given port. It seems to no longer function. No lights, no logging on the console, nothing.

To find out what's going on you simply need to know the port number on the switch. If you don't know it, you can find it by checking the error status of all known interfaces. It's as easy to solve this issue (if you simply want to bring it back up).

You type what's in italics.


From the console:
enable

Enter the following commands:
show interfaces Fast 0/1

This shows the below error:

FastEthernet0/1 is down, line protocol is down (err-disabled)
  Hardware is Fast Ethernet, address is 0011.5cc5.7481 (bia 0011.5cc5.7481)
  MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec, 
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  Auto-duplex, Auto-speed
  input flow-control is off, output flow-control is off
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 6d22h, output 6d22h, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 0 bits/sec, 0 packets/sec
     3258984 packets input, 214895633 bytes, 0 no buffer
     Received 3258780 broadcasts (0 multicast)
     0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog, 3257687 multicast, 0 pause input
     0 input packets with dribble condition detected
     1003 packets output, 104543 bytes, 0 underruns
     0 output errors, 0 collisions, 1 interface resets
     0 babbles, 0 late collision, 0 deferred
     0 lost carrier, 0 no carrier, 0 PAUSE output
     0 output buffer failures, 0 output buffers swapped out

To display all interfaces with that status:

show interfaces status err-disabled

To solve this problem and bring the interface into a useable state enter these commands:

config
interface FastEthernet 0/1
shutdown
no shutdown


You will now have:

FastEthernet0/1 is up, line protocol is up (connected)
  Hardware is Fast Ethernet, address is 0011.5cc5.7481 (bia 0011.5cc5.7481)
  MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec, 
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  Full-duplex, 100Mb/s
  input flow-control is off, output flow-control is off
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 00:00:07, output 00:00:00, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 0 bits/sec, 0 packets/sec
     3259565 packets input, 214949344 bytes, 0 no buffer
     Received 3259332 broadcasts (0 multicast)
     0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog, 3258034 multicast, 0 pause input
     0 input packets with dribble condition detected
     1250 packets output, 130215 bytes, 0 underruns
     0 output errors, 0 collisions, 3 interface resets
     0 babbles, 0 late collision, 0 deferred
     0 lost carrier, 0 no carrier, 0 PAUSE output
     0 output buffer failures, 0 output buffers swapped out

Obviously you need to change the interface to be the one that actually has the errors.