Looks like you had two partitions, I would say one was Windows or something, and then, you had problems with the partition and it disappeared.
If you can backup to a external or something using Carbon Copy or similar, and reparation by selecting 1 partition and then applying. You'll get back your space. If you had Windows or something running on another partition you could go into Windows and select it, and re-init it, just that part. THere are other things you can do, many Linux Partition Boot Disks, where you could get a GUI, and init just the hidden part.
The thing is with Disk Utility, they don't give you any help Graphically (GUI) with free space like that. You can use terminal commands and get to that free space, there are plenty of tutorials out there on Disk Utility in terminal, that talk about reclaiming free space. Hmm here is one:
http://apple.stackexchange.com/ques...-partition-in-unallocated-space-with-diskutil
Not fun, I would just back up to an external, boot off of it Reformat, RePart, ReInit, and clone back...
EOL