I recently started having issues with my secondary (slave) hard drive. I started getting 'file or directory inaccessible' errors. After a reboot, I could not access the drive at all and got the error 'file or directory is corrupted and unreadable'. So, following some other advice, I tried changing the drive letter in the disk manager, but this failed, and it is no longer even recognized as a formatted drive. Using the disk manager again, it wanted to initialize the disk, but I cancelled this as I wasn't sure if this would wipe out the MBR that was already on there or not.
This is on Windows 7 Ultimate, and the drive is a Western Digital 250GB.
Initializing the drive will destroy the data... worse than it is now anyhow. It's time for a new drive. If disk management can see the drive, you might be able to get some of the data back with recovery software.
I would clone your drive, sector by sector, with a tool (eg ddrescue freeware) that understands how to work around bad patches in the media, and then use data recovery software on the clone.
Data recovery professionals will tell you that using SpinRite on a drive with failing heads is a very bad idea. Not only will SpinRite accelerate the failure of a bad head (by repeatedly hammering away at bad sectors), but even if it is able to recover a particular sector, it then writes the data back to the bad drive.
Ddrescue is a multipass cloning utility that keeps a log of bad sectors. It clones the easy sectors on the first pass, and then tries for the more difficult ones on subsequent passes. It skips over bad patches in the media rather than flailing away pointlessly. It can also clone the drive in reverse, effectively disabling lookahead caching.
Well, I booted up SpinRite, and it couldn't do anything to the drive. It said it could not read sector 0. I shut the computer down, and I'm going to let the drive cool down, and then maybe try connecting to a different computer and see if it will see it.