logon problem with windows server 2003

iam the network adm of a window server 2003.when i wanted to logon,it prompt me for an activation and i did that.but instead for the system to enter windows proper becos i wanted to work in the control panel,it was going back to Welcome to Windows(press ctrl+alt+del)window. iam tired and i need to resolve that quikly.can anybody pls help.thanks.