I'd suggest that this is a localised problem with your system.
First port of call should be your graphics card drivers and or an uninstall/reinstall of Dreamweaver.
Your page changes should preview in the Dreamweaver interface, just like the oder versions of that program. The fact that they don't would point to either a graphics card issue or Dreamweaver's interaction with your graphics system
Would you mind posting again with details of your operating system and graphics card ?