Vista - Vista Forgets File Sharing

I recently purchased an enclosure for a two year old hard drive in order to use it to back up files between computers on my home network. I have been doing this successfully for years with a Smart Drive that is now full. Both these hard drives are attached to the same one year old Dell laptop with Vista Home Premium SP1. With the new drive, I set the drive to be shared and it works just fine until the computer and the harddrive are both turned off. When the computer is restarted, the hard drive is no longer shared, ie the setting changed. If the drive is turned off and then back on without restarting the computer, the drive is still shared, so to me, it appears that Vista isn't remembering the settings for this hard drive. I tried these same steps on our other computer which is a XP based Dell laptop and the sharing settings work properly every time. Any help would be appreciated.