Lot more information needed to answer your question.
What version of Premiere Elements are you working with and on what computer operating system it is working?
Where and when do you get this program message that codecs are not installed? Have you gotten a GSpot utility readout, showing Audio Name Codec and Status.
What are the properties of the file that you are trying to import into the project? Where is the audio from (iTunes)? MP3 or WAV file extension?
We will be watching for your follow up.