The answer is well-known: The user account into which Office 2007 is
installed lacks sufficient file access permissions.
Unlike earlier versions of Office, the 2007 Office System starts from
shortcuts that detect whether the Office program in question is fully and
correctly installed (based on your selections during the original
installation.) If Office can't determine whether it's been fully and
completely installed, it installs itself again.
If the user account into which Office is installed lacks permission to
access the files that Office needs to query, Office can't tell if its been
fully and completely installed.
Since file access permission is black magic to most users, the first and
easiest way to solve the problem is to reset all file access permissions to
their default values. This is most easily done with Microsoft's SubInACL
utility. Instructions are on the web, where they are explained in detail.
Most of the time, the above procedure works...but not always, depending on
your individual situation. That's why it helps to post the details of the
error from Event Viewer, which often helps to pinpoint the exact problem.
Since Event Viewer often makes about as much sense to the average user as
file permissions, the one solution that always works is to do a clean
install of Windows and then, before doing anything else, to install Office.
If you're wondering why Office checks itself, it's because users -
particularly in the workplace - often fiddle with their software and mess it
up. Office 2007 puts all the pieces back together.
Daddy