Reset Mac Function Keys

There's a couple of things:

1. Apple Menu -> System Preferences -> Keyboard
2. Untick "Use All F1, F2, etc keys as standard keys"
3. Click "Keyboard Shortcuts"
4. Click "Restore Defaults"

That should fix the problem.

Edit:

Some people suggest powering off the MBP, or resetting the SMC completely. Here's a forum thread which describes a similar situation.

Here's how to reset the SMC on most recent Apple Portables.

The SMC is responsible for some system IO functions, such as the trackpad, as well as power management functions. It's entirely possible that your keyboard isn't behaving because of this SMC.

Also, does this behavior occur under a new user account? If it does not, I would be inclined to trash any files from the first user's library related to keyboard - or simply migrate to the new user account, whichever is easier.

Go to System Preferences and click Keyboard. There is an option to switch the behavior.