From the Premiere Elements Information FAQ http://forums.adobe.com/thread/1042180
•What version of Premiere Elements? Include the minor version number (e.g., Premiere Elements 12 with the 12.0.1 update).
•What operating system? This should include specific minor version numbers, like "Mac OSX v10.6.8"---not just "Mac"
•Has this ever worked before? If so, do you recall any changes you made to Premiere Elements, such as adding Plug-ins, brushes, etc.? Did you make any changes to your system, such as updating hardware, printers or drivers; or installing/uninstalling any programs?
•Are you using an account with Administrator Privileges?
Run as Administrator http://forums.adobe.com/thread/969395 (Encore + "All" Premiere)
•Have you installed any recent program or OS updates? (If not, you should. They fix a lot of problems.)
•What kind(s) of image file(s)? When talking about camera raw files, include the model of camera.
•If you are getting error message(s), what is the full text of the error message(s)?
•What were you doing when the problem occurred?
•What other software are you running?
•Tell us about your computer hardware. How much RAM is installed? How much free space is on your system (C:) drive?
And some other questions...
•What are you editing, and does your video have a red line over it BEFORE you do any work?
•Which version of Quicktime do you have installed?