Sprint HTC Hero :: Media Volume Stopped Working - No Sound

Last night I was bored and browsing through my soundboards looking for a new ringtone. I was opening and closing apps, running task killer, if I thought it necessary. Everything was fine, until all of a sudden my media volume stopped working. On screen, while I'm playing media, I can pull the volume up and down, but no sound comes out. The Alarm volume, and ringer volume continue to work. So this morning I snooped around the forums and decided to reset my phone. All was going well, until I accidentally played some mp3's that were on my SD card. Now the media volume has stopped working again and when I turn on my phone, my music app has attached itself to that screen that you have to pull down to log in.

I didn't request that, and can't find a way to turn that off in the settings. To be honest, I am a new user. I've had my hero for two weeks, and I'd love to know that my problems are user error and not a faulty phone. I've also re-downloaded task killer and am wondering if that was a bad choice. I'm still at the point of just playing with my phone: launching apps, installing, uninstalling, etc, and it seemed like a good idea. In a worst case scenario, I'm thinking of deleting the mp3's and doing another reset. But if I have to keep doing this regularly, the exercise will get a little old.