USB Device not accessible

I have a Maxtor HD with 3 partitions in an external HD USB 2.0 enclosure. I hadn't had any problems with it until a few months ago when it started giving me the message that it couldn't disconnect, and I would get this message almost every time I used the drive. Probably as a result of having to shut it down without safely disconnecting, I had a few issues with data getting corrupted and having to repair files and indexes with chkdsk.

Last night, I connected the drive to move the files off of it onto a different drive so I could stop using it altogether. One of the partitions was not accessible. It showed up in the drive list, but when I clicked on it, XP reported that it needed to be formatted. I had gotten this error before and was able to fix it with chkdsk, so I just decided to copy over the other 2 partitions, and worry about this one later. I only had time to copy over the other 2 partitions.

I attempted to safely shut the drive down last night, but got the message that it couldn't disconnect. I logged off and back on and tried again, but I got the same message. So, I got impatient and shut my computer down, then turned off the external drive.

When I tried to connect to the drive today, XP would give me the usual sound when I connected it, but the drive letters never showed up in my drive list, and the drive doesn't show up in Disk Management. I tried to run chkdsk on the drive, but of course that didn't work because none of the logical drives are accessible. I restarted the computer, disconnected and reconnected the drive, etc. with the same results. Each time I attempted to safely remove the drive throughout all this, I have been able to disconnect safely.

When I look at Device Manager, Mass Storage Device shows up under USB controllers, and the drive shows up under Disk Drives. When I right click on the drive, select the Volumes tab and click the Populate button, I get the following:

Type: Unknown
Status: Unreadable
Partition Style: Not Applicable
Capacity: 0 MB

The Volumes list is blank.

I'm thinking the master boot record may be corrupted on the drive, but I don't want to attempt an mbr fix unless someone who knows more than me agrees. Does this make sense? If not, what else could the problem be?