Php display instabillity

I am working on a guestbook. The problem is that sometimes it displays fine and sometimes it looks all messed up. Right now it looks like this.

Im pretty new to the game so maybe I should of posed in newbies. I just dont know where to begin.

I'm sorry, my psychic powers have left for the day. Is there any code you could post to give us something to work with?

Ash