Stargazer: This meay be a dumb reply but I thot I would tell you of my experience. I have three external drives and they all work but not together. When one is running, I often cannot access one of the others. ESpecially if they are plugged into the same hub. Try turning off any other device on that hub, including the external drive, diconnect the USB cable, wait a few seconds, then re-apply power to the drive and, after it is up to speed, plug in the usb cable . This usually works for me... Sounds too simple but.....what can you lose??
OR Geek's idea sounds good. I used a PCI USB card in my old machine for years. Cheap, simple, and reliable..