Hi shaalini,
Unlike in Windows NT Server, Windows NT Workstation's log-in screen has a "Shutdown" button which you can use to shutdown the system without ever logging in. Here's how to disable Windows NT Workstation's "Shutdown" button on the initial log-in screen:

1)Run "Registry Editor" (run "RegEdit.exe" or "RegEdt32.exe")

2)Select the following key:

HKEY_LOCAL_MACHINE\
SOFTWARE\Microsoft\Windows NT\
Current Version\Winlogon


3) Add a value named "ShutdownWithoutLogon" of type "REG_SZ" and set it to "0".

4)Restart Windows

__________________
A.Rajesh Khanna