dio's right, the drive itself might be about to fail. Any drive can fail at any time, usually at the least opportune moment (it's an old law, or charter, or something), which is why a solid automated backup strategy is vital. Corruption of the volume's directory is more likely, although if it's bad enough then data recovery, while possible, may not be financially viable (depends on what you've lost!). If DU can't rebuild the directory and get you up and running again, then try Disk Warrior. I don't know what bad reports of DW you've read, but in my book it's the disk utility of choice for OS X. One of it's great features is that it won't actually make any changes on the drive until you tell it to do so. Other utilities get stuck in, make changes, and then find that they can't finish the job. But by this time the utility has rendered the drive unrecoverable, or only recoverable by way of a very expensive data recovery service. (We're talking $Thousands here!). In particular, have nothing to do with Norton. TechToolPro4 is good, but always use Disk Warrior first and only then, if it can't do the job (rare, and you have to be patient, it can take hours), let TTP4 have a go. If the volume in question holds only OS and App's, then the fastest solution might be to bite the bullet, initialize the drive and reinstall the software. Yeah, I know, there are authorization issues if you do that, only you can know if it's a good idea.