You're welcome mmmf, and welcome to Vista Forums.
Well, this problem is usually associated with using a registry cleaning program that was improperly allowed to delete certain registry entries. This cannot be blamed on Microsoft since this problem is caused inadvertently by the computer user and a 3rd party program.
We all make mistakes though.

Originally Posted by
mmmf
When I try the reg script that I downloaded to the desktop, I get a message saying that this cript can only be run from within the Registry.
Can you advise?

When you download and save the reg file to the desktop, does it have a icon that looks like this?
If not, then the default association for the
.reg file extension has been changed. In Method Two of this tutorial, you will need to
.reg (Name) file extension back the Current Default of
Registry Editor (C:\Windows\regedit.exe).
Default Programs
Hope this helps,
Shawn