When you use the Windows Search Assistant (click on Start, Search) to find files or folders. By default your search does not find hidden or system files. This means that you may not be able to find certain files even though they exist on whatever drive you are searching.

Here's an easy method to ensure that you do pickup those hidden files in the search.

Click on Start, Search, and then click on All Files and Folders. Enter the name of whatever you are searching for. Now click on More Advanced Options, and click to place a check mark next to Search Hidden Files and Folders. Now click on Search.