Go to your control panel or Administrative Tools and access Services. Check the Indexing Service to ensure it is running. If it is not running, start it.
If you don't find the Indexing Service then go to Add or Install Programs and select Windows Components. Select Indexing Service and go through the Wizard to install it.
I am not sitting in front of a Vista machine right now so I don't have the exact steps. However, if you need them, I can update the post later today.