The problem with pre-made external hard drives is that you don't know if the problem lies in the case, the hard drive itself, or in the connection between them. I would NEVER recommend buying a pre-made one, if not for the higher price, then for the problems (like this) that are harder to fix.
However, it could be the IDE cable connecting the drive to the IDE-Firewire bridge. If you can open up the case and make sure both the IDE cable and the power cable are plugged into the hard drive securely, it eliminates that much of the problem. Another possibility is that the hard drive itself is somehow in bad shape, and since you bought it through Fantom, you'll have to talk to them about getting it fixed/replaced (another reason why I prefer making my own; you deal directly with the drive manufacturer instead of going through a third party).
It sounds like a hardware problem to me, not something that will necessarily be fixed by merely reformatting the drive. However, I'd still recommend backing up all the data that is stored on the drive to CDs or DVDs or whatever you can. If you don't, you'll likely lose all of it.