For whatever reason, ever since I got my iMac back from having its power supply replaced, it gives me the following error message when I plug in my external firewire HD: You have inserted a disk containing no volumes that Mac OS X can read. To use the unreadable volumes, click initialize. To continue with the disk inserted, click continue. And I can't use Disk Utility on it, as it does not recognize the drive (I did not hit "continue" or "initialize"; wanted to wait to see what you guys said). What's the deal?