Sidebar/comment form dissappear

I am trying to piece together something for the other teachers at my school. I have run into a problem I can’t solve. (warning: I am a bit of a PHPnoob, so talk slow!)

I am using 1.5, but I am forgoing themes. I haven’t even uploaded the themes folder. I am using the index/wp-header/wp-footer/wp-sidebar setup with a style sheet I began using several months ago. Everything looks fine on the front page and in category pages and archive pages. But if you view one post, neither the comment template nor the sidebar appears. I have used this format before and haven’t experienced a problem. Any suggestions for what I may be overlooking?