Jeff recently updated to the Windows 2004 Feature Pack and now all his data has disappeared. He's also nearly out of space now. Leo says that's normal, as Windows saves the old version under windows.old. He can delete it or roll back to the previous version with it. But that doesn't solve his lost data issue. Fortunately, the data was backed up on an external drive, and Leo says that most problems like this have happened with people with external drives attached. Leo also adds that updating Windows is like changing an engine while an airplane is flying. It's not only a hard thing to do but rather crazy considering there are so many hardware configurations and billions of users. Even one user in 100,000 would cause 1,000 issues like this. And that's a lot.
And it's inexcusable for Microsoft to do that to someone. It's possible that his data is still there, but it's been hidden or moved. Do a search for specific files to see if he can find them. It may also be his profile is corrupted.
Always backup BEFORE an update. Always. But don't rollback. Eventually, Microsoft is going to force it, even though there isn't anything worth updating for most people. Moving forward, it will be required.