I had this same problem. It showed up after I did a factory reset. Before that all was fine and I could play music from my sdcard. I managed to "fix" it by downloading a new music player from the Android market - Android Music Player. I ran that app and it immediately found all my music. Then, when I went back and ran the built-in Music widget it too could now see all my music. It suggests there is some hidden setting for the built-in player that cannot be set/reset through the menu, but the AOSP player I downloaded was able to reset it for me. Anyhow, I hope this works for you.
I know this is an old thread, but after I experienced this myself I finally stumbled across the answer:
All music must be in a sub folder in the "Music" folder. So for instance: sdcard2/Music/Artist/song.mp3
umm... "internal card"? "external card"?
i'm new to the Rezound, so these terms have me scratching my head. I just bought a 32GB SD card, to replace the 16GB card that came with the phone. how can I put music on it such that I can play it through the Music app?
(I'm already getting the notion that only .mp3 files are supported -- is that accurate?)
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On my old Droid X I had to dismount and remount the SD card for the phone to pick up changes made to it. Maybe the Rezound is the same? The simple thing to do is just reboot the phone, that will do the same thing...
I just started having this problem today. I went into the stock music player and it showed I had 3 songs. I restarted my phone and my songs showed up. A couple of hours later I went back and it was doing the same thing. I don't know why it is all of a sudden giving me problems. I am copying my music off of my sd card and putting on the internal to see if that fixes it.