strange Yosemite sound issue

[frippy]

my mac is a 2013 imac running yosemite
but i have an odd sound issue
when i want to reduce sound level, my screen gets rolled up
but the sound stays the same
do i have to reinstall, or is there a way to switch this?
sounds challenged greg

 

[Partron22]

Rolled up to what, an entrance to the void, or something recognizable but wrong? If this is via keyboard, check keyboard prefs for an unwanted remap. You might try checking the "show sound in menu bar" option in System, Sound prefs. See what happens when you use that menu to change volume.