Hold shift + Alt (mac?) while rebooting Premiere until welcome screen.
This clears preferences and plugin cash or
Import this project into a new project, see if that helps.
>no troubles until I added some still jpgs
Some people have no problems with pictures, other people do have problems... the below MIGHT help
Pictures that are "overly" large may cause video editing problems
Photo Scaling for Video http://forums.adobe.com/thread/450798
-PPro Crash http://forums.adobe.com/thread/879967
Thanks for both of your responses.
Unfortunately neither worked. I've now updated CS6, installed CS7, updated my graphics drivers, created new projects with new files, transcoded the files, resized the images, and no visuals will playback in the Program monitor.
I'm beginning to get a bit nervous! Any other suggestions would be greatly appreciated - my clients are beginning to get a bit antsy!
You report that you installed CS7 but make no mention of applying the update. Please try it if you haven't already.