If somehow you no longer have an IP address assigned to your computer you can perform a simple renew operation by using Start > Run > type "cmd" and press Enter.
You will notice that a window with a black background will open from where you type: ipconfig /release which will clear all addresses from the available network adapters then use the same command but with /renew string, something like: ipconfig /renew and wait 1-2 minutes max then your computer will get its IP back if you use a DHCP server for lease requests.
If you have a STATIC IP address, then you will need to contact your local administrator.
