It's your HTML formatting, remove the data from the header and footer areas of the control panel and it'll be fixed. I viewed your html source of your site and there are quite a few problems with your additions.
As for the issue with your admin file, it's throwing an 500 error, you'll need to look into your webserver logs to ascertain as to why it's giving an error. Sometimes it can be because of the directory having improper chmods; I'd advise making the admin directory 777 and files in it 666.
