When finish the program, the process, Microsoft office fail, is there a dialog box, saying, must be reinstalled.

It's not related. It's just a coincidence.

There are bugs in Windows Installer that cause this, and it doesn't just happen to Office. It happens extremely frequently to Hewlett-Packard's packages (such as TrayApp and PhotoGallery), Office, and a few other vendor's packages (Earthlink's TotalAccess, for instance).

I've also had several other programs "trigger" this event, such as CCleaner, Spywareblaster, and Office itself.

You'll have to uninstall and reinstall Office to get it to work again.
You may have to use MSICUU to clean up any remaining Office packages (after you officially uninstall) :
http://support.microsoft.com/kb/290301