Just to be clear, are you saying you enter find mode, pick a value off the drop down list, click perform find, and get no results when there should be records? And you done this before and it worked, and now it doesn't?
Can you describe you value list and the field formatted with it in more detail?
What value list format are you using? Check boxes? Radio buttons? drop down list? Pop up menu?
What data type is the field? Number or text? (check in Manage | Database | Fields)