Volume is locked?

My volume is locked on my macbook air, meaning I can't change the volume, in the system preferences it's showing "no input/output devices found" and there is not red light coming out of the headphone jack, I've also tried plugging headphones in 5 or 6 times and no luck. This has been happing quite a few times now and I have no idea what to do, I've reset the PRAM and at first it worked but now it hasn't been working, so I'm kinda lost on how to fix this