Missing Hard Drive Space

Probably, Boot Camp Assistant resized the OS X volume, so you lost space, but it didn't create the Windows volume, so you have free space that it's not partitioned.

Follow these steps to resize the OS X volume and recover the original space > http://pondini.org/OSX/DU4.html

If you don't see the free space when you are going to resize the OS X volume, the hard drive was damaged and you lost that space

That means that Boot Camp Assistant didn't create the Windows volume, but it doesn't mean that the space is lost. Follow the steps of the link of my first comment.

To recover the space, follow these steps:

1. Open Disk Utility and select your hard disk at the top of the Disk Utility's left sidebar.

2. Go to Partition tab and you will see a bar like this:

The grey part is unused space. To add the space to the OS X volume, just press "Macintosh HD" at the bottom right corner and drag it to the bottom of the bar. Finally, press "Apply" and you will recover that space

In that case, you have lost that space. I recommend you to verify the hard disk to search errors and repair it, if it's needed. Then, do the same with the "Macintosh HD" volume.

If this doesn't work, you have to live without that space, or put another hard disk

Something has happened with the hard disk. Try holding Command, Option (Alt) and R keys while your Mac is starting, in order to start in Internet Recovery instead of Recovery HD, and repair the hard disk.

If it doesn't work, use the Mac OS X Install Disc that came with your computer. You can start from it holding the C key while your Mac is starting. You can find Disk Utility on the Utilities menu, after starting from this DVD

Take immediate steps to backup your data. Do this before you do anything else.

Pete