What version of Photoshop Elements? Include the minor version number (e.g., Photoshop Elements 9 with the 9.0.3 update).
Have you installed the recent updates? (If not, you should. They fix a lot of problems.)
What operating system? This should include specific minor version numbers, like "Mac OSX v10.6.8"---not just "Mac".
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?
Has this ever worked before? If so, do you recall any changes you made to PSE, 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?