View post and preview post errors

Hi there,
I am having another problem, this time with view and preview posts. If I try to preview a post before publishing, or if I try to view the single post, the only thing that comes up is the heading and post footer and nothing in between, i.e. the body of the post is missing.

I would really appreciate some assistance with this, as I haven’t the first clue as to how to go about resolving it.

Many thanks,
Jude