Today I noticed while trying to use the keyboard shortcut to enter single user mode that Mid-2012 MacBook Pro 13 Inch did not make the startup sound when turned on. After rebooting normally it still did not make the sound. The volume was turned up all the way and the internal speakers work fine. Nothing is plugged into the headphone jack. How do I turn it back on?
You can try resetting the chime back it it's defualt settings; this is done in NVRAM.
Using Terminal issue the command
sudo nvram -d SystemAudioVolume
You will be asked for your password; enter it. Reboot. You should hear the chime.