External HDD Connection (WD 500GB My Book) Conflicting With Additional USB Devices

When my External HDD (usb) is connected to my PC and I try to connect another usb device on another port at the same time like an Ipod, usb stick, or SD Card, the External HDD always makes the additional usb device unrecognizable. And when a usb device is already connected, and I connect the External HDD, the External HDD always makes my PC disconnect from the other usb device. If I unplug the External HDD and a usb device is plugged in, the PC recognizes the other usb device right away. This sucks because all of my music is stored on my external hard drive and I currently have to use my internal drive as a middleman to transfer my songs to my Ipod or SD Card. Any comments or suggestion would be much appreciated???