Do you have an IP address?

I find that the lack of an IP address is one of the best indications of why you cannot see or communicate with the network. If you do not have an IP address there is a follow-up question you can ask. Am I using DHCP? If you are using DHCP and do not have an address, there are a few things that that could mean. Either you are not connected to the network, the DHCP server is not connected to the network, or the DHCP server is not giving you an address. To fix the problem, make sure your computer is connected to the network and run the following command:

bash# /etc/rc.d/init.d/network restart
Shutting down interface eth0:                              [  OK  ]
Setting network parameters:                                [  OK  ]
Bringing up interface lo:                                  [  OK  ]
Bringing up interface eth0:                                [  OK  ]

If everything says OK then you should have an IP address. To see the IP address, type:

bash# ifconfig
eth0      Link encap:Ethernet  HWaddr 01:23:45:67:89:AB  
          inet addr:1.2.3.4  Bcast:1.2.3.255  Mask:255.255.255.0
          IPX/Ethernet 802.2 addr:CD956500:00C0F0407A8B
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:1920018 errors:0 dropped:0 overruns:0 frame:0
          TX packets:349874 errors:5 dropped:0 overruns:0 carrier:5
          collisions:0 txqueuelen:100 
          Interrupt:11 Base address:0x1000 

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:23510 errors:0 dropped:0 overruns:0 frame:0
          TX packets:23510 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0

In this example the IP address is 1.2.3.4. If you still do not have an IP address you can try to configure a static IP address using linuxconf, netconf, netcfg, or netconfig.