Katie, if you are using the default browser of Windows 7, it's Internet Explorer. Depending on the version you are using, just emptying the cache might not be enough to remove the cached redirect that is causing the error when you click on the User CP link.
1. Did you actually empty the browser cache or is it possible that you might have emptied your browsing history instead? I ask because you mentioned history
. These are two different things.
2. If you did empty your browser cache and restarting the browser didn't help - you can still not access the User CP - could you try this workaround
which is specifically for Internet Explorer?
I am sorry for the inconvenience. I wish we had known before about the consequences of improperly using 301 redirects.