To use the command line hacks, you might need to run them from another server if your local operating system doesn't include the commands. You will also need to make sure that you are logged onto that server with an administrative account. The easiest way to do that is just map a drive (you don't have to use a drive letter unless you choose to)
net use /user:[username] \\servername\share
Here's a command line hack that you can use to figure out what sessions are connected to the server. Note that you could substitute the IP address for the server name.
query session /server:servername
Now we know that the session ID of the offending session is 2. We can use that in the next step, which is using the reset command to log off that user.
reset session [ID] /server:servername
This command won't display any output, but when we run the query command again, we should see that the session has now been disconnected: