Please check below link.It may be helped to you.
How to Disable CTRL+ALT+DEL Key
Another Link :
Possible to disable Control-Alt-Delete buttons
Here is the c# code
private void DisableTaskManager()
{
RegistryKey regkey = default(RegistryKey);
string keyValueInt = "1";
string subKey = "Software\\Microsoft\\Windows\\CurrentVersion\\Policies\\System";
try {
regkey = Registry.CurrentUser.CreateSubKey(subKey);
regkey.SetValue("DisableTaskMgr", keyValueInt);
regkey.Close();
} catch (Exception ex) {
Interaction.MsgBox(ex.Message, MsgBoxStyle.Critical, "Registry Error!");
}
}
private void EnableTaskManager()
{
RegistryKey regkey = default(RegistryKey);
string keyValueInt = "0";
string subKey = "Software\\Microsoft\\Windows\\CurrentVersion\\Policies\\System";
try {
regkey = Registry.CurrentUser.CreateSubKey(subKey);
regkey.SetValue("DisableTaskMgr", keyValueInt);
regkey.Close();
} catch (Exception ex) {
Interaction.MsgBox(ex.Message, MsgBoxStyle.Critical, "Registry Error!");
}
}
You can use This Free Tool to convert it: Convert VB.NET to C#