If your control panel appears without styling, first check to make sure that your themes folder exists, and contains /cp_themes/default/default.css and the accompanying images folder.

If those files are present and complete, the server you are on my have PHP running with an open_basedir restriction.  In these cases, that restriction prevents PHP script files from accessing anything that resides in directories above its path.  The solution is to move the cp_themes folder into your system folder.  Do not move your entire themes folder, just the cp_themes folder.  ExpressionEngine will automatically discover it, and your Control Panel will then be styled properly.