PLEASE HELP Site customize is no longer working

My sites customize is no longer working. Sometimes when it comes up it will stick at the "loading" but the left side panel for drag and drop never shows, and the other times it will just show the website front end and nothing else.

Also, ive noticed that 8 times out of ten, when i try and log in to my site, it redirects, and then just stays on the login page and does not log me in. Any ideas on why these too things are happening?

Thank you
Laura