Why isn't search working in Finder?

Other than your Finder having jaundice, this should be a simple fix. The following command will clear the volumes local store and rebuild it if necessary; Open up Terminal and type:

# sudo mdutil -E /

• You will be asked for your password, provide it, as this command requires administrator privileges to run.
• After confirming your Spotlight index will be re-built and your files should appear in the search. ( Depending on the size of your HDD it can take a while )

To check if all volumes have indexing enabled or disabled use:

# mdutil -s -a

To toggle (enable/disable) indexing on all volumes:

# mdutil -a -i

These commands are safe to use when/if you encounter similar issues as described in the question.

Complete options available:

 -p  Spotlight caches indexes of some network devices locally.  This option requests
     that a local caches be flushed to the appropriate network device.

 -E  This flag will cause each local store for the volumes indicated to be erased.
     The stores will be rebuilt if appropriate.

 -i on | off
     Sets the indexing status for the provided volumes to on or off.  Note that index-
     ing may be delayed due to low disk space or other conditions.

 -s  Display the indexing status of the listed volumes.

 -a  Apply command to all volumes.

 -v  Print verbose information when available.

• mdutil(1) Mac OS X Manual Page

Being as the UI is a better way to go than to jump right away into Terminal, try the following from Apple's support documentation:

1. From the Apple menu, choose System Preferences.
2. Click Spotlight.
3. Click the Privacy tab.
4. Drag a folder or even an entire volume (your hard drive) to the list.
5. Remove the item or volume you just added.

Failing these steps and the steps advised by the others, try creating a new user and seeing if search works in Finder. If it still does not work, then search is broken system-wide and an Archive & Install will not help. You'll want to back up your data and reinstall the OS. If an Apple Store is close, they can be of assistance here (no charge).