A collague and I were doing some work on our MOSS system, at the same
time... Like an idiot, I made a change to core.css by going right to the
physical file on the drive on the server, instead of checking it out
through Designer like I should have... or, instead of just adding a
style definition to the master page... anyway, our root-level URL now
returns the message:

HTTP/1.1 404 Connection: close Date: Mon, 15 Oct 2007 15:37:02 GMT
Server: Microsoft-IIS/6.0 X-Powered-By: ASP.NET
MicrosoftSharePointTeamServices: 12.0.0.4518

...and when we try to open the site using Designer, it displays the
error message:

Server error: The URL
sisu.sisunet.org/_vti_bin/_vti_aut/author.dll
<sisu.sisunet.org/_vti_bin/_vti_aut/author.dll> is not contained
within a Windows Sharepoint Services site

There are other web apps/site collections on the server that run just
fine, but the root is having some serious issues. I've replaced core.css
with the original file, which didn't make any difference at all after
restarting IIS. If anyone has any thoughts as to how we might be able to
rescue this site, I'd be most grateful!