I messed up my tumblr theme and now I can't get it back to normal?

So on Tumbler I got tired of using themes out of the theme garden so I started using themes that people made and in the end they ended up...not working and now I'm trying to go back to using the themes from the theme garden and it keeps showing up in the same form of this same theme, just in different colors. I've tried switching from enabling custom HTML code, to disabling it, and I don't know what to do, help?