I've lost the power button from my Vista Start Menu

A couple of days ago something odd happened to my Vista ultimate setup:
1) I discovered that I could nolonger access task manager - "this operation has been cancelled due to restrictions in effect on this computer."
2) I could nolonger access registry editor - (see above message).
3) The power button was nolonger on the start menu, and when I try to shut down using the alt + f4 command I'm presented with the same message (see above message).

Now I've managed to claw back access to task manager and regedit using some scripts I found on websites but i've been unable to restore the power button to the start menu.

I've tried to go into group policy editor - gpedit.msc and enable the start meny power button to no avail - it makes no difference.

I've done countless virus and spyware checks with different programs and nothing has come up. :

My PC doesn't seem to be operating any less effectively.

Temporarily I've created shortcuts to shut down, hibernate and restart my PC but I'd really like the button on the start menu back.

Any help in this regard would be much appreciated