Have you tried removing the disk then reconnecting the USB/Firewire cable with Windows open to see if it re-recognises it, or tried the disk on another computer? I'd also boot a linux liveCD like Knoppix to see what that makes of the disk too Though unlikely these days, it could also have been the work of a virus

On the bright side, anime is the easiest to recover since there's so many places to redownload it from, and probably in higher quality this time round