This may seem like a stupid question, but did you back everything up? I would rather assume you did since--to my recollection--repartitioning with DU is destructive--wipes your data. I hear tell from the youn'uns with their fancy hotrods, bebop and Mountain Lion that this may not be the case.
IF you backed everything up, I would suggest simply starting again--erase the HD and then try to repartition it.
IF you did not----then the question is where is your data. If it is in the partition you can access, run along to your local convenience store/crackhouse that sells Ex-HDs, get one--if you do not already have one--and clone that. This way, you do not lose anything as you try to repair what happened. If that is successful--and it is something you should do routinely --then simply erase and repartition then clone back "you" from your clone to the partition you wanted.
IF you have data on the partition you cannot access I would suggest:
1. Back up what you have not backed up which you can access.
2. Consider booting from an External HD--sure, you can use your recovery partition but then you are "on" your regular HD which you have problems with. Much faster and easier to be booted off of another drive. If you can do that--see advantages to cloning--then try to repair the drive from the External.
If that does not work then you have two other options:
1. Wait for a Guru who can figure out some more technical way to work through what happened--he may want crash logs and the like.
2. Consider a program like Disk Warrior--$$ but has saved volumes that otherwise cannot be saved. It may create a virtual disk of your data which you can then move over/save to your Ext-HD thereby allowing you to start all over again with erase and repartition.