You create a project, you export its Timeline to a MPG file, presumed Share/Computer/MPEG - what preset, and do you go with the default settings of the preset or customize it under the Advanced Button/Video Tab of the preset? If you customized the preset's settings, what did you set under Video, Audio, and Multiplexer tabs?
Several weeks later, can I presume that you want to upload to YouTube
a. the MPEG file from the computer hard drive to YouTube at the YouTube web site
b. the Timeline of the original project using the Premiere Elements built in YouTube feature
Where is the file not playing back with sound - in the YouTube player, via a computer player, or other?