Disk Utility works forever at trying to repair partitions
Disk Utility repair functions are (from what I have heard) just a front end to FSCK, so that will likely give you the same results. You could try another disk repair utility (diskWarrior, techtool, etc...), or if you have a recent backup I would be tempted to wipe the drive and start over.

If you have another Mac you could put that Mac into target disk mode, connect the two via Firewire or Thunderbolt and try the repair that way.

It is possible that the drive itself is damaged and beyond repair. The problem here is that disk utility is usually not smart enough to know when to give up. And repairs can take a long time (overnight is not unheard of) so unrecoverably damaged disks often initially diagnose similar to what you are seeing.

Failing other disk utilities or other Macs your best bet might be a visit to an Apple Genius. they will diagnose you for free, repairs may cost you if you are out of warranty.