Question: The volume on my macbook pro has suddenly become greyed out. I haven't installed any updates or made any modifications to the computer, it just suddenly became greyed out after waking the macbook up from sleeping.

I've tried resetting the PRAM, but I don't hear any chime at all when I start up my computer, no matter how long I wait/how many times the computer re-restarts itself.

There also seem to be no internal speakers detected when I go into system preferences. For both input and output the computer detects 0 devices.

Thanks so much in advance for any help!!

Answer: 
I had no output from speakers, or headphones. And the System Preferences - Volume was greyed out.

I tried everything up to including a PRAM reset and nothing worked.

Took it to the company tech and after awhile he figured out what was wrong.

The inner head phone jack was dirty. He cleaned it with a qtip or a special computer cleaning device. Apparently there’s a internal sensor in the jack that will prevent the internal output from functioning if it’s to dirty. It’s not like a dropped the computer in a dirty pond. I would have never figured that out.

Anyways, that’s what fixed it for me with the same symptoms as listed.
I had this same problem with my MacBook Pro, and used the technique described by dennismuys. I inserted and removed my headphone plug about a dozen times, and the internal speakers started working again. I have no idea what could possibly have gotten in the jack to keep the switch from closing. Lint maybe.