I found myself needing to disable the CTRL+ALT+DEL login on a remote server because our support client "was not allowed to inject CTRL+ALT+DEL via software because of system policy".
To get around this I ran a change on the registry via command line (The support tool did let me have CMD access..).
Here is the easy way to do it. (Put the following into a cmd window. This will also work if you are already loaded into the system. Make sure to reboot after for it to take effect).
(This worked for me, make sure you get the correct slashes.)
reg add "HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Policies\System" /v DisableCAD /t REG_DWORD /d 1 /f
(Some mentioned that the above might not work and suggested the folowing as well)
REG ADD "HKEY_LOCAL_MACHINE\Software\Microsoft\CurrentVersion\Policies\System /f /v DisableCAD /t REG_WORD /d 1
Note that you will have to reboot the server once you run the above before it takes effect!
shutdown /r /t 005
(The above will reboot the server after 5 seconds).