Ok, I had this problem as well. I got it back by accident...
For some reason all of the music on my usb drive is stuffed ito the "other" category under "genres".
Press "music type", then select "other".
You now should be enjoying your music in alpanumeric order.
Then press the "RND"(random) button.
It now should be playing all the music randomly.
This should work unless your music is actually assigned to a specific genre.
Worked for me. Hope it works for you all too!