Vista - Windows programs not opening

Hi

I have Vista Ultimate

I cannot open operating system programs, like UAC and Windows update in
Control Panel, defender will not update and Windows Update in the Start menu
will not open,

When I click on the links a window opens for an instant then disappears.

I tried System restore and the issue remains, rebooting, hard or soft does
not help either.

I have Windows firewall, defender and AVG antivirus installed and running
and a scan of each and Spybot and Adaware has found nothing

Any ideas on how to fix this?

thanks

Daniel