No guarantees, but it's worth a try. It won't hurt anything, I promise. Boot your computer while holding command, option, p, r. Let it chime 4 times. Then hold command, option, o, f while booting. When you get to a text prompt, type reset-nvram and press enter. Then type reset-all and hit enter again. The computer will reboot and I'll bet a small amount of money your volume keys will work properly.