Vista - Shutdown options missing from logon

Hi all
After the last update cycle through Windows update I'm experiencing a
strange thing: the red shutdown button on the downright of the logon screen
has disappeared : I googled for some solutions but all those that I found
belong to XP (I cant find a
"HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer"
on my machine's registry) .I preferably won't roll back to a previous
restore point because many programs need to be reinstalled after I do that,
especially Pinnacle studio which I have experienced it has a tough
installation.The shutdown has proved to be useful after important updates
because I can avoid errors with restarts. Can anybody drive me to a solution
?
Thx very much for your help!
M