Automatic logon problems in NT 3.51

We are running a SCADA package on an NT 3.51 machine at a mine. Since we often have power failures, the PC reboots itself and then requires the operator to type in the password. We wanted to change this so that the PC is automatically logged on as user OPERATOR and restarted the SCADA.

After some research, I found out how this could be done via the registry. In HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindows NTCurrentVersionWinLogon I added a value called AutoAdminLogon of type REG_SZ and value = 1, as well as DefaultUserName = OPERATOR and DefaultPassword = operator’s password. This prevents the Logon screen with CTRL-ALT-DEL when logging on, and simply logs on as OPERATOR. This is fine; however, now the problem…

How do you now log on as the Administrator, which needs to be done to make changes to the SCADA system? NT always logs on as OPERATOR, who has no rights to make changes to the SCADA or registry, so I am stuck being user OPERATOR. Even logging off simply causes automatic logon to start again. Unlike NT4, NT3.51 does not have the option to “Close all programs and log on a different user.” What can I do ?

Another good reason to go to NT 4.0. Outside of reinstalling NT (and setting up the OPERATOR with rights to those keys), here is the approved MS way:

“To stop the auto logon, you need to do so from another Windows NT computer. First, log on to another Windows NT computer. Then, start a command prompt and connect to your auto logon computer via:”

"net use : \c$ user:administrator

where is an available drive letter and is the name of the auto logon computer. You will then be prompted for the administrator password for that computer. After you enter that password and successfully log on, run REGEDT32 and choose the Select Computer item from the Registry menu. This brings up a dialog box that lets you remotely edit the Registry of the auto logon computer. Type the name of that computer to change and disable the auto logon feature. The next time you start your auto logon computer (turn it off and then on again, not just a logoff/logon), the auto logon will not happen.”

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