Sound completely disappeared after exporting video

[jannn]

I spent hours to make a video only to find out that after I exported, the background song I used is completely gone. I went back to edit screen and works perfectly fine, so I have no idea what happened. I was using a 7 day trial and this was my last export (3/3) so I'm very disappointed that I won't be able to fix and export. The other two videos I made were perfectly fine and I didnt change any export settings either. Huge disappoinment. 

[Steve Grisetti]

Please be sure to include what device and operating system you are editing on the source and resolution of your video.

[jannn]

Asus Zenbook UX305F, Windows 10, 1080