FIND utility won’t find

On XP Home edition PC I wanted to find my Outlook .pst file. In the Find utility I typed *.pst (I may have renamed the file from Outlook.pst to something else) and check the boxes for Search Hidden Files and Search System Folders, and specified AllHard Disks to search in. Find found 0 files, but of course I have two .pst files somewhere. Why won’t Find find?