Q: the volume and brightness keys not working?

Try going to system preferences/keyboard, keyboard tab, make sure that Use all F,F2 etc keys as standard function keys is not checked

Try a SMC reset:

http://support.apple.com/kb/HT3964

pram reset:

http://support.apple.com/kb/HT1379

You can try a safe mode boot, sometmes it will fix glitchy things:

Power holding the shift key, continue to hod the shift key till you see the progress BAR then release and allow to finish booting (note this will take longer than usual, as will the shut down)

After it boots it should say safe mode in red on the screen, log in, log out and shut down. Restart normally.

All the best

You are welcome, glad to have helped

You have a great day as well.

I have the same problem, except in my case it's not only the volume and screen brightness buttons, but also the backlight and eject buttons that don't work.

I've tried smc reset, pram reset and safe mode boot, but none of these fixes worked for me.

Any suggestions that don't involve re-installing the OS?

Thank you for mentioning this!

Same situation happened to me, using "El Capitan" 10.11.2 with a MacBook Air.

After the safe reboot mentioned here, the keys worked okay again !

Thank you and best regards !

I know this is a super late reply, but I came across this post looking for answers and I hope this answer helps someone else that may have this problem. Like the above person said, I went to my keyboard preferences and made sure that the "use all F1, F2 etc. keys as standard function keys" checkbox wasn't checked, and it wasn't. But I realized I had the checkbox below it checked that says "adjust keyboard brightness in low light." When I pressed the backlight adjusting keys, it would come up like it usually does when it adjusts brightness, but instead of the brightness level it showed a circle with a line through it. When I unchecked that box it worked fine. Just in case someone else accidentally checked that box and their keys wouldn't adjust brightness anymore, here's how I fixed it!