Finding out template
You are looking for Theme developer module:


  Firebug for Drupal themeing. See the screenshot and screencast. Note that this module injects markers into the DOM to do its magic. This may cause some themes to behave erratically and less capable browsers may make it worse (especially IE)/. Enable it when needed, and disable it afterwards. 






If it is crashing your website

You need to upgrade. You are at 7.0, current version is 7.31. You are 31 minor versions behind. And some of them was security updates. So you probably should upgrade anyway.