netsh

www.computerhope.com/netsh.htm

netsh interface show interface

to show the interface name which for me was "Ethernet 2" and then:

netsh interface set interface "Ethernet 2" DISABLED
netsh interface set interface "Ethernet 2" ENABLED

Under Windows XP there is a small feature allowing you to repair a network 

connection. Go to the Network Connections options in Control panel 

(Control Panel / Network Connections), right click on the network connection 

you want and choose the repair option.

It is possible to run the same command by using the Netsh utility, 

within the following command line:

netsh int ip reset c:\network-connection.log

c:\network-connection.log represents the address of the file in which 

the reporting will be stored

The netsh int ip ...command allows you to reset the TCP/IP.

With Windows XP Service Pack 2, you can use:

netsh winsock reset catalog

Resetting the socket which manages the TCP/IP. This can be used to handle 

network problems (browser problem, IP address related problems, etc ...) 

Create a batch file ( I called mine netrepair.bat) and place it in a directory where you have execute permissions. Use notepad to create the file.
type the following lines in the file
ipconfig /renew arp -d * nbtstat -R nbtstat -RR ipconfig /flushdns ipconfig /registerdns
then save and close.
Open a cmd terminal as administrator, navigate to the folder on which netrepair.bat is saved and then type
netrepair.bat
at the command line.
That's it.
Refer to http://support.microsoft.com/kb/289256 for explanations of what the commands do