Okay this is a problem I was having with my Galaxy Nexus and now my Note 2 as well. Basically when going to settings to try to turn the media volume back up the slider is locked and won't move. I have been searching the forums and have found that many people are having this issue with their Galaxy devices.
With my nexus it primarily happened when I was trying to watch a video (Youtube a vine or whatever) My fix to this was to just go to Pandora or Play music and it would start back up.
With the Note 2 I have to reboot the device and then it started working again.
I was trying to find an APP to attribute the issue to, and on my nexus I thought it was Ruzzle (a boogle like game ) but I don't even have it downloaded on my Note 2 so I have no idea what is the cause of it.
Another way that I have found works on resetting the media sound is to plug in headphones and start music or a video and then pull them out, the sound should be restored as well.
Any feedback on what anyone thinks the culprit APP is or a permanent fix to this chime in. As I said I found that there have been other people with this issue and thought I would try to address it.