Sometimes the best way to get rid of problems with a hard drive is to reformat it. If I were you I would do some back up of anything you dont want to loose from your HD, then start up from the disc that came with your computer and reformat using Drive Setup. Also, if your going to install the Mac OS X beta it's a good idea to partition your HD giving the beta at least 1.5 GB of space if you haven't already. That's just my suggestion.