I have the same problem – I’m with streamline.net. They keep insisting I’m to blame or it’s to do with plugins, even though i’m sure it’s a problem there end.
I did find a plugin you can use as a work around (if you ever mange to login) – http://ww.wp.xz.cn/plugins/rename-wp-login/ –
it changes the login url (so it can be yoursite.com/login rather wp-login.php which seemed to work for one of my effected site).
It still doesn’t solve the problem of actually logging in in the first instance.
Rest assured, it looks like it’s almost certainly a hosting issue and nothing to do with you or your site.
Its maybe a htaccess problem. Just in case consult your host support.
503 errors are permissions errors. They tend to only show up when there is either a hosting configuration problem (e.g. if your web host is pointing your web address at the wrong folder on your hosting account) OR when the permissions on the files and folders are wrong.
For most web hosts, file/folder permissions for normal files/folders (e.g. probably not for sensitive files like .htaccess and wp-config.php) are:
files: 644
folders: 755
If you notice that the wp-admin folder has different permissions than that or that the index.php file in that folder has different permissions than that, that is probably a factor.
Otherwise, you would want to talk with Dreamhost tech support.
503 errors are not permission errors, that is absolutely incorrect.
503 Service Unavailable
The server is currently unavailable (because it is overloaded or down for maintenance). Generally, this is a temporary state.
http://en.wikipedia.org/wiki/List_of_HTTP_status_codes
