Don't turn it off.
My home network consists of four XP Pro PCs. File and printer sharing set up, everything works perfectly. To make backing up easier I connected a USB-2 external HD to my main PC and set it for sharing. Was going to drag and drop what I wanted to save to a folder for each PC. Worked great. Until I powered it off. Now it's not shared anymore.
No big deal, just wondering why it won't stay shared.