I have a 1.4TB Seagate Free Agent external hard drive that will disconnect and then reconnect a few seconds later, and does this about every 20 or 30 minutes. Even when I'm not accessing the drive or using the computer it does this. I dual boot XP and Vista and it does this in both. My first thought was to try a different cable, but the problem persisted. However when I tried the drive with my laptop I had no problems whatsoever. Given the symptoms I'm gonna take a guess that it's a hardware problem, but more than that I have no idea.