Main Page blank

I know there are already hundreds of posts, but I couldnt find the solution for my problem there.

My main page/blog page is balnk. the rest seems to work fine.
I tried disabling all plugins to no avail and when I switch themes its back. So it has to be in the theme folder, right?
Before the big scary blank I installed YARPP and was just installling a custom template which makes it necessary to add lines to style.css.
I undid that right after i saw what had happened, but the page is still all white.
Any ideas? Should I delete the theme and re-install?