SSL Problem

Hi, I installed an SSL certificate on my server and now trying to use a plugin (really simple SSL) to complete the process. When I activate SSL the site ends up completely broken.

The plugin tells you 'Some things can't be done automatically. Before you migrate, please check for:
Http references in your .css and .js files: change any http:// into //
Images, stylesheets or scripts from a domain without an SSL certificate: remove them or move to your own server.'

Please advise!