What are you doing with the program when it is using all available CPU?
Closed - Opened?
If opened project....project preset, properties of sources media, extent/complexing of editing and size of projects, burn to and/or
export to file saved to computer hard drive scope?
Description of computer and its resources?
Thanks for posting on Adobe forums.
Please try to update Premiere Elements 12 to Premiere Elements 12.1
Let us know if this help.