TFS file must remain locked
If you don't want to delete the workspace, you can undo the change and unlock the file after that:
Using a Visual Studio developer command prompt:
tf undo "$/<server-path-to-file/folder>" /workspace:"<workspace>;<user>" /collection:<collection-url> /recursive
tf lock "$/<server-path-to-file/folder>" /lock:none /workspace:"<workspace>;<user>" /collection:<collection-url> /recursive
Undoing the lock won't work on those files because they are binary, as binaries cannot be merged they must be locked if they are checked out.
As the machine the workspace resides on no longer exists (the machine has been renamed) the best thing to do is delete the workspace.
from a Visual Studio command prompt
tf workspace /delete oldmachine;myusername /collection:http://*tfsserver*:8080/tfs/*collection*
This will remove the workspace and undo all pending changes