Without exact info on comp settings, render settings, system specs and so on nobody can tell you anything. From simple hardware issues to wrong render settings this could be anything.
If you are having trouble rendering then first - read the help files on Rendering. Follow the advice given in the help files for the kind of file you want to export. Since you are combining audio from different tracks you should also read the help files on working with audio. You'll find the index to After Effects Help here.
If you are a complete beginner then read the getting started with After Effects information available on the home page of this forum. Using After Effects is a lot like flying an airplane. Without taking the time to get some instruction and do some studying you are destined to do things wrong the first time and end up in trouble.
If none of this works you'll have to give us the info that Mylenium asked for because there are probably a billion ways to set up a project and at least a million ways to do it incorrectly.
I never change the comp settings from the default settings, except for with and height, as for render settings I've formatted it as a quick time movie and Avi. File with audio out put on 44.100 kHz 16 bit stero, I'm using a hp pavilion 20 with windows 8