I ran into this problem when i changed my SD card.
I found out why ar first a scan or full scan does not work for some people and what fixed it for me.
If from inside Poweramp go to settings >> library. From there you can try a scan if that does not work before you try a full scan you might want to try this easy fix, as full scan may cause you to lose some things like tags.
Under Full Scan, go into the Music Folder Tab. If like my case you will the SD card icon is unchecked. I guess Poweamp saw it was missing when i changed it.
Since all my music is on my SD I unchecked all others. Once I left the SD as the only source to scan, Poweramp automatically scanned the card on its own.
Hope this helps get your music back!
