Hi,
Try to Rebuild the index
1. Click Start, in the Search box, type Indexing, and open Indexing Options under Control Panel.
2. Click Advanced, click the Index Settings tab, and then click Rebuild. If you are prompted for an administrator password or confirmation, type the password
or provide confirmation.
If it still not works, try to use following method.
Step 1: Check registry settings
1. Click Start, in the Search box, type regedit and press Enter to open the registry editor.
2. Locate the following registry subkeys:
HKEY_LOCAL_MACHINESoftware\Policies\Microsoft\Windows\Search\PreventIndexingOutlook
HKEY_LOCAL_MACHINESoftware\Policies\Microsoft\Windows\Search\PreventIndexingEmailAttachments
3. Please first back up the registry subkeys above. Then, check if the value data is set to 1. If it is, please change it to 0, or delete the registry subkey.
For more information, you can also refer to the following article:
http://technet.microsoft.com/en-us/library/cc178983.aspx
Hope that helps.