Every time I start my Mac, there's no output device listed in system preferences > audio. In order to fix this, I have to reset SMC several times. I also tried to reset NVRAM. However, if I turn off the Mac and start it again the next day, the same problem appears again. This problem first occurred, after I installed soundflower. But I uninstalled it already. I'm using Mac Mini late 2012 with common Logitech loudspeakers.
When I run Apple Hardware test, it outputs this result: