I posted a few days ago & didn’t get a reply.
Originally, my problem was that once I masked out an area (eyebrows/eyelashes) where I wanted fibers, and clicked on the “preview” button, my model would disappear from my view completely. It would say up top how many fibers it created, but the model would be completely invisible until I either clicked on the screen or unpressed the “preview” button. I’ve used fibermesh before, it just recently started doing this.
Now, I’m having the problem where the model isn’t disappearing when I push the preview button, the fibers just aren’t showing up on the screen, even though it says they’re there. I tried just putting in settings, accepting it and rendering it and they definitely aren’t there, even though the subtool for hair is there on the side of my screen.
Has anyone else had a problem like this? Is there anything I can do to fix it? It’s really frustrating, because I’d love to give my character eyelashes, eyebrows and even hair. 
Another issue I’ve had in the past when I was able to actually produce hair on another model, was that if I combed it in symmetry, one side would work and the other side would just…disappear–so I couldn’t use symmetry to style (it was even messed up when I rendered it to look at it)
Please help! I’m getting frustrated and it’s been doing this for over a week.
PS~I have an iMac, if that means anything. I was using an old macbook when it started making my model disappear, and it continued to do the same after getting my new computer a week ago.