I have cleared my cookies, cache, and tried the Default and the IPS Default themes, but all of them when I go to http://shroudofgossamer.com/admin/ I get the following screen:

 

Looks like the admin folder does not exist on your server there or if you have a custom admin directory, you are missing the constant for it.

There is an admin folder.

What do you mean by "missing the constant for it"?

Unfortunately, your server is not serving files from that directory as it is resulting in a 404 error. You have a lot of items in your .htaccess file, you may wish to simplify that to see why. If you're still having issues, please contact your hosting provider.