“Everytime I open my computer before I log in there is error message “a duplicate name exist on the network”. I already change the computer name on the properties then change computer name. then when I re-start my Computer nothing happen. still the error appears before I log in.
You should check you are actually changing the name. Open the Control Panel by clicking Start, Settings, Control Panel and then click System.
In the System properties click the Computer Name tab. This is where you may be being misled as the “Computer Description” box is different to the computer’s name. The actual name is below under the “Full Computer Name” heading.
To change this, click the “Change” button. Choose a name different to all the other computers on the network and put this in the Computer name box. Keep clicking okay until the computer says it needs to restart and let the computer reboot.
This should clear the problem. If it doesn’t click Start, Run and type ipconfig /flushdns. This should wipe the computer’s memory of other addresses and should get rid of the message on restart.