On what operating system is your Premiere Elements 12 running on?
Are you in the Expert workspace? Assuming so, what is the video and audio tracks (including Narration and Soundtrack) setup?
Did you include Smart Mix and/or Audio Mixer in your workflow.
Other questions about project settings will come next if necessary, including formats of videos, pixel dimensions of photos, formats of music files, et al.
Is this a "it worked before but not now" or "it never worked before" type issue?
Depending on your answers, a screenshot the opened Smart Mix/Audio Mixer dialog might prove helpful.