disappearing PowerPoints

I have a lab of 28 computers where PowerPoints are randomly disappearing. It does not happen on all computers or even all users on a computer. The PowerPoints were there the last time the student worked on it but isn’t there now. It was saved and even shows in recent documents but it is no where to be found. They are using MS Office 2003 Professional with latest serice pack and the computers are running windows xp with sp3. This is not happening in other labs and the only difference is the other labs are using a different version of office or office 2003 standard. I have searched all files/folders including system and hidden. I ran an undelete utility but can’t find anything. Does anyone have any ideas or suggestions?