Technical Difficulties :(

So, I'm just throwing this out there in hopes for some help but....

why won't Blogger let me change to my own custom template (layout) for the background? Every time I try and use a template that is not provided by Blogger, the HTML is all messed up and won't display the layout correctly. I know it's not something I'm doing wrong (I happen to have a tech whiz for a boyfriend) and I know that it's not the layouts I've tried using. Any suggestions or insight? Much appreciated!