The answers will be in the details. At this point you have not supplied us with adequate information to help you.
The information needed would include:
1. What version of Premiere Elements are you working with and on what computer operating system is it running?
2. What are the properties of what you have on the project's Timeline...video and audio compressions, frame size, frame rate, interlaced or progressive, file extension, pixel aspect ratio, duration?
3. The project settings should match the properties of the source media, so what did you or the project set as the project preset for this project?
4. Can we assume that the video has audio that could be heard while it was played back in the Edit area? In other words, did the Timeline content loss it audio only after it was exported?
5. How did you export the Timeline content? Share/? or Publish+Share/? what preset and did you customize the settings under the export's Advanced Button/Video Tab and Audio Tab?
6. What player are you using to determine the video and audio qualities of your export?
7. How would you characterize this issue "it worked before but not now" or "it never worked before"?
Lots of questions.
Please review the above. If you need clarification on anything written, please do not hesitate to ask.