Query Builder not available

The Query Builder is not available to me in Outlook. When I expand it, all the fields are grayed out.
How can I enable it?

Components for the Query Builder are not part of Outlook but part of Windows Desktop Search (WDS). As long as you don’t have WDS installed, the Query Builder will not work.

WDS is included by default in Windows Vista and Windows 7. However, it is not a part of Windows XP. Usually when Outlook detects that WDS is not installed, there will be an Infobar showing under the Instant Search box stating; “Click here to enable Instant Search”.
Clicking on that link will take you to the download page of WDS. However, since you can turn this notification off, Windows XP users can download it here and the latest version for other Windows versions can be found here.

If you just want the Query Builder to work and do not want Windows Desktop Search to index your emails, then you can exclude your mailbox from being indexed by going to;
Tools-> Options…-> button Search Options…-> deselect all the locations you do not want to index.

In addition you can choose to disable the Windows Search Email Indexer add-in. For more on how to disable add-ins see this post.

To prevent any other location on your computer from being indexed by WDS, see this post.

Note: If you are in a corporate environment and are not allowed to install anything on your PC, then you can use Advanced Find as an alternative. To open Advanced Find use CTRL+SHIFT+F or Tools-> Instant Search-> Advanced Find…